app/email_handler.py

"""
Handle the email *forward* and *reply*. phase. There are 3 actors:
- contact: who sends emails to alias@sl.co address
- SL email handler (this script)
- user personal email: to be protected. Should never leak to contact.

This script makes sure that in the forward phase, the email that is forwarded to user personal email has the following
envelope and header fields:
Envelope:
    mail from: @contact
    rcpt to: @personal_email
Header:
    From: @contact
    To: alias@sl.co # so user knows this email is sent to alias
    Reply-to: special@sl.co # magic HERE

And in the reply phase:
Envelope:
    mail from: @contact
    rcpt to: @contact

Header:
    From: alias@sl.co # so for contact the email comes from alias. magic HERE
    To: @contact

The special@sl.co allows to hide user personal email when user clicks "Reply" to the forwarded email.
It should contain the following info:
- alias
- @contact


"""
import argparse
import email
import time
import uuid
from email import encoders
from email.encoders import encode_noop
from email.message import Message
from email.mime.application import MIMEApplication
from email.mime.multipart import MIMEMultipart
from email.utils import formataddr, make_msgid, formatdate, getaddresses
from io import BytesIO
from smtplib import SMTPRecipientsRefused
from typing import List, Tuple, Optional

import newrelic.agent
from aiosmtpd.controller import Controller
from aiosmtpd.smtp import Envelope
from sqlalchemy.exc import IntegrityError

from app import pgp_utils, s3
from app.alias_utils import try_auto_create
from app.config import (
    EMAIL_DOMAIN,
    URL,
    UNSUBSCRIBER,
    LOAD_PGP_EMAIL_HANDLER,
    ENFORCE_SPF,
    ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
    ALERT_BOUNCE_EMAIL,
    ALERT_SPAM_EMAIL,
    SPAMASSASSIN_HOST,
    MAX_SPAM_SCORE,
    MAX_REPLY_PHASE_SPAM_SCORE,
    ALERT_SEND_EMAIL_CYCLE,
    ALERT_MAILBOX_IS_ALIAS,
    PGP_SENDER_PRIVATE_KEY,
    ALERT_BOUNCE_EMAIL_REPLY_PHASE,
    NOREPLY,
    BOUNCE_EMAIL,
    BOUNCE_PREFIX,
    BOUNCE_SUFFIX,
    TRANSACTIONAL_BOUNCE_PREFIX,
    TRANSACTIONAL_BOUNCE_SUFFIX,
    ENABLE_SPAM_ASSASSIN,
    BOUNCE_PREFIX_FOR_REPLY_PHASE,
    NEWRELIC_CONFIG_PATH,
)
from app.email import status
from app.email.rate_limit import rate_limited
from app.email.spam import get_spam_score
from app.email_utils import (
    send_email,
    add_dkim_signature,
    add_or_replace_header,
    delete_header,
    render,
    get_orig_message_from_bounce,
    delete_all_headers_except,
    get_spam_info,
    get_orig_message_from_spamassassin_report,
    parseaddr_unicode,
    send_email_with_rate_control,
    get_email_domain_part,
    copy,
    to_bytes,
    send_email_at_most_times,
    is_valid_alias_address_domain,
    should_add_dkim_signature,
    add_header,
    get_header_unicode,
    generate_reply_email,
    is_reply_email,
    normalize_reply_email,
    is_valid_email,
    replace,
    should_disable,
    parse_id_from_bounce,
    spf_pass,
    sl_sendmail,
    sanitize_header,
    get_queue_id,
    should_ignore_bounce,
)
from app.extensions import db
from app.log import LOG, set_message_id
from app.models import (
    Alias,
    Contact,
    EmailLog,
    User,
    RefusedEmail,
    Mailbox,
    Bounce,
    TransactionalEmail,
    IgnoredEmail,
)
from app.pgp_utils import PGPException, sign_data_with_pgpy, sign_data
from app.utils import sanitize_email
from init_app import load_pgp_public_keys
from server import create_app, create_light_app

# forward or reply
_DIRECTION = "X-SimpleLogin-Type"


_EMAIL_LOG_ID_HEADER = "X-SimpleLogin-EmailLog-ID"
_ENVELOPE_FROM = "X-SimpleLogin-Envelope-From"
_ENVELOPE_TO = "X-SimpleLogin-Envelope-To"

_MIME_HEADERS = [
    "MIME-Version",
    "Content-Type",
    "Content-Disposition",
    "Content-Transfer-Encoding",
]
_MIME_HEADERS = [h.lower() for h in _MIME_HEADERS]

newrelic_app = None
if NEWRELIC_CONFIG_PATH:
    newrelic.agent.initialize(NEWRELIC_CONFIG_PATH)

    newrelic_app = newrelic.agent.register_application()


# fix the database connection leak issue
# use this method instead of create_app
def new_app():
    app = create_light_app()

    @app.teardown_appcontext
    def shutdown_session(response_or_exc):
        # same as shutdown_session() in flask-sqlalchemy but this is not enough
        db.session.remove()

        # dispose the engine too
        db.engine.dispose()

    return app


def get_or_create_contact(from_header: str, mail_from: str, alias: Alias) -> Contact:
    """
    contact_from_header is the RFC 2047 format FROM header
    """
    contact_name, contact_email = parseaddr_unicode(from_header)
    if not is_valid_email(contact_email):
        # From header is wrongly formatted, try with mail_from
        if mail_from and mail_from != "<>":
            LOG.w(
                "Cannot parse email from from_header %s, parse from mail_from %s",
                from_header,
                mail_from,
            )
            _, contact_email = parseaddr_unicode(mail_from)

    if not is_valid_email(contact_email):
        LOG.w(
            "invalid contact email %s. Parse from %s %s",
            contact_email,
            from_header,
            mail_from,
        )
        # either reuse a contact with empty email or create a new contact with empty email
        contact_email = ""

    contact_email = sanitize_email(contact_email)

    contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)
    if contact:
        if contact.name != contact_name:
            LOG.d(
                "Update contact %s name %s to %s",
                contact,
                contact.name,
                contact_name,
            )
            contact.name = contact_name
            db.session.commit()

        # contact created in the past does not have mail_from and from_header field
        if not contact.mail_from and mail_from:
            LOG.d(
                "Set contact mail_from %s: %s to %s",
                contact,
                contact.mail_from,
                mail_from,
            )
            contact.mail_from = mail_from
            db.session.commit()

        if not contact.from_header and from_header:
            LOG.d(
                "Set contact from_header %s: %s to %s",
                contact,
                contact.from_header,
                from_header,
            )
            contact.from_header = from_header
            db.session.commit()
    else:
        LOG.d(
            "create contact %s for alias %s",
            contact_email,
            alias,
        )

        try:
            contact = Contact.create(
                user_id=alias.user_id,
                alias_id=alias.id,
                website_email=contact_email,
                name=contact_name,
                mail_from=mail_from,
                from_header=from_header,
                reply_email=generate_reply_email(contact_email, alias.user)
                if is_valid_email(contact_email)
                else NOREPLY,
            )
            if not contact_email:
                LOG.d("Create a contact with invalid email for %s", alias)
                contact.invalid_email = True

            db.session.commit()
        except IntegrityError:
            LOG.w("Contact %s %s already exist", alias, contact_email)
            db.session.rollback()
            contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)

    return contact


def get_or_create_reply_to_contact(
    reply_to_header: str, alias: Alias
) -> Optional[Contact]:
    """
    Get or create the contact for the Reply-To header
    """
    name, address = parseaddr_unicode(reply_to_header)

    if not is_valid_email(address):
        LOG.w(
            "invalid reply-to address %s. Parse from %s",
            address,
            reply_to_header,
        )
        return None

    address = sanitize_email(address)

    contact = Contact.get_by(alias_id=alias.id, website_email=address)
    if contact:
        return contact
    else:
        LOG.d(
            "create contact %s for alias %s via reply-to header",
            address,
            alias,
            reply_to_header,
        )

        try:
            contact = Contact.create(
                user_id=alias.user_id,
                alias_id=alias.id,
                website_email=address,
                name=name,
                reply_email=generate_reply_email(address, alias.user),
            )
            db.session.commit()
        except IntegrityError:
            LOG.w("Contact %s %s already exist", alias, address)
            db.session.rollback()
            contact = Contact.get_by(alias_id=alias.id, website_email=address)

    return contact


def replace_header_when_forward(msg: Message, alias: Alias, header: str):
    """
    Replace CC or To header by Reply emails in forward phase
    """
    new_addrs: [str] = []
    headers = msg.get_all(header, [])
    # headers can be an array of Header, convert it to string here
    headers = [str(h) for h in headers]
    for contact_name, contact_email in getaddresses(headers):
        # convert back to original then parse again to make sure contact_name is unicode
        addr = formataddr((contact_name, contact_email))
        contact_name, _ = parseaddr_unicode(addr)

        contact_email = sanitize_email(contact_email)

        # no transformation when alias is already in the header
        if contact_email == alias.email:
            new_addrs.append(addr)
            continue

        if not is_valid_email(contact_email):
            LOG.w("invalid contact email %s. %s. Skip", contact_email, headers)
            continue

        contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)
        if contact:
            # update the contact name if needed
            if contact.name != contact_name:
                LOG.d(
                    "Update contact %s name %s to %s",
                    contact,
                    contact.name,
                    contact_name,
                )
                contact.name = contact_name
                db.session.commit()
        else:
            LOG.debug(
                "create contact for alias %s and email %s, header %s",
                alias,
                contact_email,
                header,
            )

            try:
                contact = Contact.create(
                    user_id=alias.user_id,
                    alias_id=alias.id,
                    website_email=contact_email,
                    name=contact_name,
                    reply_email=generate_reply_email(contact_email, alias.user),
                    is_cc=header.lower() == "cc",
                    from_header=addr,
                )
                db.session.commit()
            except IntegrityError:
                LOG.w("Contact %s %s already exist", alias, contact_email)
                db.session.rollback()
                contact = Contact.get_by(alias_id=alias.id, website_email=contact_email)

        new_addrs.append(contact.new_addr())

    if new_addrs:
        new_header = ",".join(new_addrs)
        LOG.d("Replace %s header, old: %s, new: %s", header, msg[header], new_header)
        add_or_replace_header(msg, header, new_header)
    else:
        LOG.d("Delete %s header, old value %s", header, msg[header])
        delete_header(msg, header)


def replace_header_when_reply(msg: Message, alias: Alias, header: str):
    """
    Replace CC or To Reply emails by original emails
    """
    new_addrs: [str] = []
    headers = msg.get_all(header, [])
    # headers can be an array of Header, convert it to string here
    headers = [str(h) for h in headers]

    for _, reply_email in getaddresses(headers):
        # no transformation when alias is already in the header
        if reply_email == alias.email:
            continue

        contact = Contact.get_by(reply_email=reply_email)
        if not contact:
            LOG.w(
                "%s email in reply phase %s must be reply emails", header, reply_email
            )
            # still keep this email in header
            new_addrs.append(reply_email)
        else:
            new_addrs.append(formataddr((contact.name, contact.website_email)))

    if new_addrs:
        new_header = ",".join(new_addrs)
        LOG.d("Replace %s header, old: %s, new: %s", header, msg[header], new_header)
        add_or_replace_header(msg, header, new_header)
    else:
        LOG.d("delete the %s header. Old value %s", header, msg[header])
        delete_header(msg, header)


def prepare_pgp_message(
    orig_msg: Message, pgp_fingerprint: str, public_key: str, can_sign: bool = False
) -> Message:
    msg = MIMEMultipart("encrypted", protocol="application/pgp-encrypted")

    # clone orig message to avoid modifying it
    clone_msg = copy(orig_msg)

    # copy all headers from original message except all standard MIME headers
    for i in reversed(range(len(clone_msg._headers))):
        header_name = clone_msg._headers[i][0].lower()
        if header_name.lower() not in _MIME_HEADERS:
            msg[header_name] = clone_msg._headers[i][1]

    # Delete unnecessary headers in clone_msg except _MIME_HEADERS to save space
    delete_all_headers_except(
        clone_msg,
        _MIME_HEADERS,
    )

    if clone_msg["Content-Type"] is None:
        LOG.d("Content-Type missing")
        clone_msg["Content-Type"] = "text/plain"

    if clone_msg["Mime-Version"] is None:
        LOG.d("Mime-Version missing")
        clone_msg["Mime-Version"] = "1.0"

    first = MIMEApplication(
        _subtype="pgp-encrypted", _encoder=encoders.encode_7or8bit, _data=""
    )
    first.set_payload("Version: 1")
    msg.attach(first)

    if can_sign and PGP_SENDER_PRIVATE_KEY:
        LOG.d("Sign msg")
        clone_msg = sign_msg(clone_msg)

    # use pgpy as fallback
    second = MIMEApplication(
        "octet-stream", _encoder=encoders.encode_7or8bit, name="encrypted.asc"
    )
    second.add_header("Content-Disposition", 'inline; filename="encrypted.asc"')

    # encrypt
    # use pgpy as fallback
    msg_bytes = to_bytes(clone_msg)
    try:
        encrypted_data = pgp_utils.encrypt_file(BytesIO(msg_bytes), pgp_fingerprint)
        second.set_payload(encrypted_data)
    except PGPException:
        LOG.w("Cannot encrypt using python-gnupg, use pgpy")
        encrypted = pgp_utils.encrypt_file_with_pgpy(msg_bytes, public_key)
        second.set_payload(str(encrypted))

    msg.attach(second)

    return msg


def sign_msg(msg: Message) -> Message:
    container = MIMEMultipart(
        "signed", protocol="application/pgp-signature", micalg="pgp-sha256"
    )
    container.attach(msg)

    signature = MIMEApplication(
        _subtype="pgp-signature", name="signature.asc", _data="", _encoder=encode_noop
    )
    signature.add_header("Content-Disposition", 'attachment; filename="signature.asc"')

    try:
        signature.set_payload(sign_data(to_bytes(msg).replace(b"\n", b"\r\n")))
    except Exception:
        LOG.exception("Cannot sign, try using pgpy")
        signature.set_payload(
            sign_data_with_pgpy(to_bytes(msg).replace(b"\n", b"\r\n"))
        )

    container.attach(signature)

    return container


def handle_email_sent_to_ourself(alias, mailbox, msg: Message, user):
    # store the refused email
    random_name = str(uuid.uuid4())
    full_report_path = f"refused-emails/cycle-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)
    refused_email = RefusedEmail.create(
        path=None, full_report_path=full_report_path, user_id=alias.user_id
    )
    db.session.commit()
    LOG.d("Create refused email %s", refused_email)
    # link available for 6 days as it gets deleted in 7 days
    refused_email_url = refused_email.get_url(expires_in=518400)

    send_email_at_most_times(
        user,
        ALERT_SEND_EMAIL_CYCLE,
        mailbox.email,
        f"Email sent to {alias.email} from its own mailbox {mailbox.email}",
        render(
            "transactional/cycle-email.txt",
            alias=alias,
            mailbox=mailbox,
            refused_email_url=refused_email_url,
        ),
        render(
            "transactional/cycle-email.html",
            alias=alias,
            mailbox=mailbox,
            refused_email_url=refused_email_url,
        ),
    )


def handle_forward(envelope, msg: Message, rcpt_to: str) -> List[Tuple[bool, str]]:
    """return an array of SMTP status (is_success, smtp_status)
    is_success indicates whether an email has been delivered and
    smtp_status is the SMTP Status ("250 Message accepted", "550 Non-existent email address", etc)
    """
    address = rcpt_to  # alias@SL

    alias = Alias.get_by(email=address)
    if not alias:
        LOG.d("alias %s not exist. Try to see if it can be created on the fly", address)
        alias = try_auto_create(address)
        if not alias:
            LOG.d("alias %s cannot be created on-the-fly, return 550", address)
            if should_ignore_bounce(envelope.mail_from):
                return [(True, status.E207)]
            else:
                return [(False, status.E515)]

    user = alias.user

    if user.disabled:
        LOG.w("User %s disabled, disable forwarding emails for %s", user, alias)
        if should_ignore_bounce(envelope.mail_from):
            return [(True, status.E207)]
        else:
            return [(False, status.E504)]

    # mail_from = envelope.mail_from
    # for mb in alias.mailboxes:
    #     # email send from a mailbox to alias
    #     if mb.email == mail_from:
    #         LOG.w("cycle email sent from %s to %s", mb, alias)
    #         handle_email_sent_to_ourself(alias, mb, msg, user)
    #         return [(True, "250 Message accepted for delivery")]

    from_header = str(msg["From"])
    LOG.d("Create or get contact for from_header:%s", from_header)
    contact = get_or_create_contact(from_header, envelope.mail_from, alias)

    reply_to_contact = None
    if msg["Reply-To"]:
        reply_to = str(msg["Reply-To"])
        LOG.d("Create or get contact for from_header:%s", reply_to)
        # ignore when reply-to = alias
        if reply_to == alias.email:
            LOG.i("Reply-to same as alias %s", alias)
        else:
            reply_to_contact = get_or_create_reply_to_contact(reply_to, alias)

    if not alias.enabled:
        LOG.d("%s is disabled, do not forward", alias)
        EmailLog.create(
            contact_id=contact.id,
            user_id=contact.user_id,
            blocked=True,
            alias_id=contact.alias_id,
            commit=True,
        )
        db.session.commit()
        # do not return 5** to allow user to receive emails later when alias is enabled
        return [(True, status.E200)]

    ret = []
    mailboxes = alias.mailboxes

    # no valid mailbox
    if not mailboxes:
        if should_ignore_bounce(envelope.mail_from):
            return [(True, status.E207)]
        else:
            return [(False, status.E516)]

    # no need to create a copy of message
    for mailbox in mailboxes:
        if not mailbox.verified:
            LOG.d("%s unverified, do not forward", mailbox)
            ret.append((False, status.E517))
        else:
            # create a copy of message for each forward
            ret.append(
                forward_email_to_mailbox(
                    alias, copy(msg), contact, envelope, mailbox, user, reply_to_contact
                )
            )

    return ret


def forward_email_to_mailbox(
    alias,
    msg: Message,
    contact: Contact,
    envelope,
    mailbox,
    user,
    reply_to_contact: Optional[Contact],
) -> (bool, str):
    LOG.d("Forward %s -> %s -> %s", contact, alias, mailbox)

    if mailbox.disabled:
        LOG.d("%s disabled, do not forward")
        if should_ignore_bounce(envelope.mail_from):
            return True, status.E207
        else:
            return False, status.E518

    # sanity check: make sure mailbox is not actually an alias
    if get_email_domain_part(alias.email) == get_email_domain_part(mailbox.email):
        LOG.w(
            "Mailbox has the same domain as alias. %s -> %s -> %s",
            contact,
            alias,
            mailbox,
        )
        mailbox_url = f"{URL}/dashboard/mailbox/{mailbox.id}/"
        send_email_with_rate_control(
            user,
            ALERT_MAILBOX_IS_ALIAS,
            user.email,
            f"Your mailbox {mailbox.email} and alias {alias.email} use the same domain",
            render(
                "transactional/mailbox-invalid.txt",
                mailbox=mailbox,
                mailbox_url=mailbox_url,
                alias=alias,
            ),
            render(
                "transactional/mailbox-invalid.html",
                mailbox=mailbox,
                mailbox_url=mailbox_url,
                alias=alias,
            ),
            max_nb_alert=1,
        )

        # retry later
        # so when user fixes the mailbox, the email can be delivered
        return False, status.E405

    email_log = EmailLog.create(
        contact_id=contact.id,
        user_id=user.id,
        mailbox_id=mailbox.id,
        alias_id=contact.alias_id,
        commit=True,
    )
    LOG.d("Create %s for %s, %s, %s", email_log, contact, user, mailbox)

    if ENABLE_SPAM_ASSASSIN:
        # Spam check
        spam_status = ""
        is_spam = False

        if SPAMASSASSIN_HOST:
            start = time.time()
            spam_score, spam_report = get_spam_score(msg, email_log)
            LOG.d(
                "%s -> %s - spam score:%s in %s seconds. Spam report %s",
                contact,
                alias,
                spam_score,
                time.time() - start,
                spam_report,
            )
            email_log.spam_score = spam_score
            db.session.commit()

            if (user.max_spam_score and spam_score > user.max_spam_score) or (
                not user.max_spam_score and spam_score > MAX_SPAM_SCORE
            ):
                is_spam = True
                # only set the spam report for spam
                email_log.spam_report = spam_report
        else:
            is_spam, spam_status = get_spam_info(msg, max_score=user.max_spam_score)

        if is_spam:
            LOG.w(
                "Email detected as spam. %s -> %s. Spam Score: %s, Spam Report: %s",
                contact,
                alias,
                email_log.spam_score,
                email_log.spam_report,
            )
            email_log.is_spam = True
            email_log.spam_status = spam_status
            db.session.commit()

            handle_spam(contact, alias, msg, user, mailbox, email_log)
            return False, status.E519

    if contact.invalid_email:
        LOG.d("add noreply information %s %s", alias, mailbox)
        msg = add_header(
            msg,
            f"""Email sent to {alias.email} from an invalid address and cannot be replied""",
            f"""Email sent to {alias.email} from an invalid address and cannot be replied""",
        )

    delete_all_headers_except(
        msg,
        [
            "From",
            "To",
            "Cc",
            "Subject",
            # References and In-Reply-To are used for keeping the email thread
            "References",
            "In-Reply-To",
        ]
        + _MIME_HEADERS,
    )

    # create PGP email if needed
    if mailbox.pgp_enabled() and user.is_premium() and not alias.disable_pgp:
        LOG.d("Encrypt message using mailbox %s", mailbox)
        if mailbox.generic_subject:
            LOG.d("Use a generic subject for %s", mailbox)
            orig_subject = msg["Subject"]
            orig_subject = get_header_unicode(orig_subject)
            add_or_replace_header(msg, "Subject", mailbox.generic_subject)
            msg = add_header(
                msg,
                f"""Forwarded by SimpleLogin to {alias.email} with "{orig_subject}" as subject""",
                f"""Forwarded by SimpleLogin to {alias.email} with <b>{orig_subject}</b> as subject""",
            )

        try:
            msg = prepare_pgp_message(
                msg, mailbox.pgp_finger_print, mailbox.pgp_public_key, can_sign=True
            )
        except PGPException:
            LOG.e(
                "Cannot encrypt message %s -> %s. %s %s", contact, alias, mailbox, user
            )
            # so the client can retry later
            return False, status.E406

    # add custom header
    add_or_replace_header(msg, _DIRECTION, "Forward")

    msg[_EMAIL_LOG_ID_HEADER] = str(email_log.id)
    msg[_ENVELOPE_FROM] = envelope.mail_from
    # when an alias isn't in the To: header, there's no way for users to know what alias has received the email
    msg[_ENVELOPE_TO] = alias.email
    message_id = make_msgid(str(email_log.id), EMAIL_DOMAIN)
    LOG.d("message id %s", message_id)
    msg["Message-ID"] = message_id
    msg["Date"] = formatdate()

    # change the from header so the sender comes from a reverse-alias
    # so it can pass DMARC check
    # replace the email part in from: header
    contact_from_header = msg["From"]
    new_from_header = contact.new_addr()
    add_or_replace_header(msg, "From", new_from_header)
    LOG.d("From header, new:%s, old:%s", new_from_header, contact_from_header)

    if reply_to_contact:
        reply_to_header = msg["Reply-To"]
        new_reply_to_header = reply_to_contact.new_addr()
        add_or_replace_header(msg, "Reply-To", new_reply_to_header)
        LOG.d("Reply-To header, new:%s, old:%s", new_reply_to_header, reply_to_header)

    # replace CC & To emails by reverse-alias for all emails that are not alias
    replace_header_when_forward(msg, alias, "Cc")
    replace_header_when_forward(msg, alias, "To")

    # add List-Unsubscribe header
    unsubscribe_link, via_email = alias.unsubscribe_link()
    add_or_replace_header(msg, "List-Unsubscribe", f"<{unsubscribe_link}>")
    if not via_email:
        add_or_replace_header(
            msg, "List-Unsubscribe-Post", "List-Unsubscribe=One-Click"
        )

    add_dkim_signature(msg, EMAIL_DOMAIN)

    LOG.d(
        "Forward mail from %s to %s, mail_options:%s, rcpt_options:%s ",
        contact.website_email,
        mailbox.email,
        envelope.mail_options,
        envelope.rcpt_options,
    )

    try:
        sl_sendmail(
            # use a different envelope sender for each forward (aka VERP)
            BOUNCE_EMAIL.format(email_log.id),
            mailbox.email,
            msg,
            envelope.mail_options,
            envelope.rcpt_options,
            is_forward=True,
        )
    except SMTPRecipientsRefused:
        # that means the mailbox is maybe invalid
        LOG.w(
            "SMTPRecipientsRefused forward phase %s -> %s -> %s",
            contact,
            alias,
            mailbox,
        )
        if should_ignore_bounce(envelope.mail_from):
            return True, status.E207
        else:
            return False, status.E521
    else:
        db.session.commit()
        return True, status.E200


def handle_reply(envelope, msg: Message, rcpt_to: str) -> (bool, str):
    """
    Return whether an email has been delivered and
    the smtp status ("250 Message accepted", "550 Non-existent email address", etc)
    """
    reply_email = rcpt_to

    # reply_email must end with EMAIL_DOMAIN
    if not reply_email.endswith(EMAIL_DOMAIN):
        LOG.w(f"Reply email {reply_email} has wrong domain")
        return False, status.E501

    # handle case where reply email is generated with non-allowed char
    reply_email = normalize_reply_email(reply_email)

    contact = Contact.get_by(reply_email=reply_email)
    if not contact:
        LOG.w(f"No such forward-email with {reply_email} as reply-email")
        return False, status.E502

    alias = contact.alias
    address: str = contact.alias.email
    alias_domain = address[address.find("@") + 1 :]

    # Sanity check: verify alias domain is managed by SimpleLogin
    # scenario: a user have removed a domain but due to a bug, the aliases are still there
    if not is_valid_alias_address_domain(alias.email):
        LOG.exception("%s domain isn't known", alias)
        return False, status.E503

    user = alias.user
    mail_from = envelope.mail_from

    if user.disabled:
        LOG.exception(
            "User %s disabled, disable sending emails from %s to %s",
            user,
            alias,
            contact,
        )
        return [(False, status.E504)]

    # Anti-spoofing
    mailbox = get_mailbox_from_mail_from(mail_from, alias)
    if not mailbox:
        if alias.disable_email_spoofing_check:
            # ignore this error, use default alias mailbox
            LOG.w(
                "ignore unknown sender to reverse-alias %s: %s -> %s",
                mail_from,
                alias,
                contact,
            )
            mailbox = alias.mailbox
        else:
            # only mailbox can send email to the reply-email
            handle_unknown_mailbox(envelope, msg, reply_email, user, alias, contact)
            return False, status.E505

    if ENFORCE_SPF and mailbox.force_spf and not alias.disable_email_spoofing_check:
        if not spf_pass(envelope, mailbox, user, alias, contact.website_email, msg):
            # cannot use 4** here as sender will retry.
            # cannot use 5** because that generates bounce report
            return True, status.E201

    email_log = EmailLog.create(
        contact_id=contact.id,
        alias_id=contact.alias_id,
        is_reply=True,
        user_id=contact.user_id,
        mailbox_id=mailbox.id,
        commit=True,
    )
    LOG.d("Create %s for %s, %s, %s", email_log, contact, user, mailbox)

    # Spam check
    if ENABLE_SPAM_ASSASSIN:
        spam_status = ""
        is_spam = False

        # do not use user.max_spam_score here
        if SPAMASSASSIN_HOST:
            start = time.time()
            spam_score, spam_report = get_spam_score(msg, email_log)
            LOG.d(
                "%s -> %s - spam score %s in %s seconds. Spam report %s",
                alias,
                contact,
                spam_score,
                time.time() - start,
                spam_report,
            )
            email_log.spam_score = spam_score
            if spam_score > MAX_REPLY_PHASE_SPAM_SCORE:
                is_spam = True
                # only set the spam report for spam
                email_log.spam_report = spam_report
        else:
            is_spam, spam_status = get_spam_info(
                msg, max_score=MAX_REPLY_PHASE_SPAM_SCORE
            )

        if is_spam:
            LOG.w(
                "Email detected as spam. Reply phase. %s -> %s. Spam Score: %s, Spam Report: %s",
                alias,
                contact,
                email_log.spam_score,
                email_log.spam_report,
            )

            email_log.is_spam = True
            email_log.spam_status = spam_status
            db.session.commit()

            handle_spam(contact, alias, msg, user, mailbox, email_log, is_reply=True)
            return False, status.E506

    delete_all_headers_except(
        msg,
        [
            "From",
            "To",
            "Cc",
            "Subject",
            # References and In-Reply-To are used for keeping the email thread
            "References",
            "In-Reply-To",
        ]
        + _MIME_HEADERS,
    )

    # replace the reverse-alias (i.e. "ra+string@simplelogin.co") by the contact email in the email body
    # as this is usually included when replying
    if user.replace_reverse_alias:
        LOG.d("Replace reverse-alias %s by contact email %s", reply_email, contact)
        msg = replace(msg, reply_email, contact.website_email)

    # create PGP email if needed
    if contact.pgp_finger_print and user.is_premium():
        LOG.d("Encrypt message for contact %s", contact)
        try:
            msg = prepare_pgp_message(
                msg, contact.pgp_finger_print, contact.pgp_public_key
            )
        except PGPException:
            LOG.e(
                "Cannot encrypt message %s -> %s. %s %s", alias, contact, mailbox, user
            )
            # to not save the email_log
            EmailLog.delete(email_log.id)
            db.session.commit()
            # return 421 so the client can retry later
            return False, status.E402

    db.session.commit()

    # make the email comes from alias
    from_header = alias.email
    # add alias name from alias
    if alias.name:
        LOG.d("Put alias name in from header")
        from_header = formataddr((alias.name, alias.email))
    elif alias.custom_domain:
        LOG.d("Put domain default alias name in from header")

        # add alias name from domain
        if alias.custom_domain.name:
            from_header = formataddr((alias.custom_domain.name, alias.email))

    add_or_replace_header(msg, "From", from_header)

    replace_header_when_reply(msg, alias, "To")
    replace_header_when_reply(msg, alias, "Cc")

    # Message-ID can reveal about the mailbox -> replace it
    message_id = make_msgid(str(email_log.id), get_email_domain_part(alias.email))
    LOG.d("make message id %s", message_id)
    add_or_replace_header(
        msg,
        "Message-ID",
        message_id,
    )
    date_header = formatdate()
    msg["Date"] = date_header

    msg[_DIRECTION] = "Reply"
    msg[_EMAIL_LOG_ID_HEADER] = str(email_log.id)

    LOG.d(
        "send email from %s to %s, mail_options:%s,rcpt_options:%s",
        alias.email,
        contact.website_email,
        envelope.mail_options,
        envelope.rcpt_options,
    )

    if should_add_dkim_signature(alias_domain):
        add_dkim_signature(msg, alias_domain)

    # generate a mail_from for VERP
    verp_mail_from = f"{BOUNCE_PREFIX_FOR_REPLY_PHASE}+{email_log.id}+@{alias_domain}"

    try:
        sl_sendmail(
            verp_mail_from,
            contact.website_email,
            msg,
            envelope.mail_options,
            envelope.rcpt_options,
            is_forward=False,
        )
    except Exception:
        # to not save the email_log
        db.session.rollback()

        LOG.w("Cannot send email from %s to %s", alias, contact)
        send_email(
            mailbox.email,
            f"Email cannot be sent to {contact.email} from {alias.email}",
            render(
                "transactional/reply-error.txt",
                user=user,
                alias=alias,
                contact=contact,
                contact_domain=get_email_domain_part(contact.email),
            ),
            render(
                "transactional/reply-error.html",
                user=user,
                alias=alias,
                contact=contact,
                contact_domain=get_email_domain_part(contact.email),
            ),
        )

    # return 250 even if error as user is already informed of the incident and can retry sending the email
    return True, status.E200


def get_mailbox_from_mail_from(mail_from: str, alias) -> Optional[Mailbox]:
    """return the corresponding mailbox given the mail_from and alias
    Usually the mail_from=mailbox.email but it can also be one of the authorized address
    """
    for mailbox in alias.mailboxes:
        if mailbox.email == mail_from:
            return mailbox

        for address in mailbox.authorized_addresses:
            if address.email == mail_from:
                LOG.debug(
                    "Found an authorized address for %s %s %s", alias, mailbox, address
                )
                return mailbox

    return None


def handle_unknown_mailbox(
    envelope, msg, reply_email: str, user: User, alias: Alias, contact: Contact
):
    LOG.w(
        "Reply email can only be used by mailbox. "
        "Actual mail_from: %s. msg from header: %s, reverse-alias %s, %s %s %s",
        envelope.mail_from,
        msg["From"],
        reply_email,
        alias,
        user,
        contact,
    )

    authorize_address_link = (
        f"{URL}/dashboard/mailbox/{alias.mailbox_id}/#authorized-address"
    )
    mailbox_emails = [mailbox.email for mailbox in alias.mailboxes]
    send_email_with_rate_control(
        user,
        ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
        user.email,
        f"Attempt to use your alias {alias.email} from {envelope.mail_from}",
        render(
            "transactional/reply-must-use-personal-email.txt",
            alias=alias,
            sender=envelope.mail_from,
            authorize_address_link=authorize_address_link,
            mailbox_emails=mailbox_emails,
        ),
        render(
            "transactional/reply-must-use-personal-email.html",
            alias=alias,
            sender=envelope.mail_from,
            authorize_address_link=authorize_address_link,
            mailbox_emails=mailbox_emails,
        ),
    )

    # Notify sender that they cannot send emails to this address
    send_email_with_rate_control(
        user,
        ALERT_REVERSE_ALIAS_UNKNOWN_MAILBOX,
        envelope.mail_from,
        f"Your email ({envelope.mail_from}) is not allowed to send emails to {reply_email}",
        render(
            "transactional/send-from-alias-from-unknown-sender.txt",
            sender=envelope.mail_from,
            reply_email=reply_email,
        ),
        render(
            "transactional/send-from-alias-from-unknown-sender.html",
            sender=envelope.mail_from,
            reply_email=reply_email,
        ),
    )


def handle_bounce_forward_phase(msg: Message, email_log: EmailLog):
    """
    Handle forward phase bounce
    Happens when an email cannot be sent to a mailbox
    """
    contact = email_log.contact
    alias = contact.alias
    user = alias.user
    mailbox = email_log.mailbox

    # email_log.mailbox should be set during the forward phase
    if not mailbox:
        LOG.exception("Use %s default mailbox %s", alias, alias.mailbox)
        mailbox = alias.mailbox

    Bounce.create(email=mailbox.email, commit=True)

    LOG.debug(
        "Handle forward bounce %s -> %s -> %s. %s", contact, alias, mailbox, email_log
    )

    # Store the bounced email, generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"refused-emails/full-{random_name}.eml"
    s3.upload_email_from_bytesio(
        full_report_path, BytesIO(to_bytes(msg)), f"full-{random_name}"
    )

    file_path = None

    orig_msg = get_orig_message_from_bounce(msg)
    if not orig_msg:
        # Some MTA does not return the original message in bounce message
        # nothing we can do here
        LOG.w(
            "Cannot parse original message from bounce message %s %s %s %s",
            alias,
            user,
            contact,
            full_report_path,
        )
    else:
        file_path = f"refused-emails/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id
    )
    db.session.flush()
    LOG.d("Create refused email %s", refused_email)

    email_log.bounced = True
    email_log.refused_email_id = refused_email.id
    email_log.bounced_mailbox_id = mailbox.id
    db.session.commit()

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"

    # inform user of this bounce
    if not should_disable(alias):
        LOG.d(
            "Inform user %s about a bounce from contact %s to alias %s",
            user,
            contact,
            alias,
        )
        disable_alias_link = f"{URL}/dashboard/unsubscribe/{alias.id}"
        send_email_with_rate_control(
            user,
            ALERT_BOUNCE_EMAIL,
            user.email,
            f"Email from {contact.website_email} to {alias.email} cannot be delivered to your mailbox",
            render(
                "transactional/bounce/bounced-email.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            render(
                "transactional/bounce/bounced-email.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            max_nb_alert=10,
        )
    else:
        LOG.w(
            "Disable alias %s now",
            alias,
        )
        alias.enabled = False
        db.session.commit()

        send_email_with_rate_control(
            user,
            ALERT_BOUNCE_EMAIL,
            user.email,
            f"Alias {alias.email} has been disabled due to multiple bounces",
            render(
                "transactional/bounce/automatic-disable-alias.txt",
                alias=alias,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            render(
                "transactional/bounce/automatic-disable-alias.html",
                alias=alias,
                refused_email_url=refused_email_url,
                mailbox_email=mailbox.email,
            ),
            max_nb_alert=10,
        )


def handle_bounce_reply_phase(envelope, msg: Message, email_log: EmailLog):
    """
    Handle reply phase bounce
    Happens when  an email cannot be sent from an alias to a contact
    """
    contact: Contact = email_log.contact
    alias = contact.alias
    user = alias.user
    mailbox = email_log.mailbox or alias.mailbox

    LOG.debug(
        "Handle reply bounce %s -> %s -> %s.%s", mailbox, alias, contact, email_log
    )

    Bounce.create(email=sanitize_email(contact.website_email), commit=True)

    # Store the bounced email
    # generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"refused-emails/full-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)

    orig_msg = get_orig_message_from_bounce(msg)
    file_path = None
    if orig_msg:
        file_path = f"refused-emails/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id, commit=True
    )
    LOG.d("Create refused email %s", refused_email)

    email_log.bounced = True
    email_log.refused_email_id = refused_email.id

    email_log.bounced_mailbox_id = mailbox.id

    db.session.commit()

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"

    LOG.d(
        "Inform user %s about bounced email sent by %s to %s",
        user,
        alias,
        contact,
    )
    send_email_with_rate_control(
        user,
        ALERT_BOUNCE_EMAIL_REPLY_PHASE,
        mailbox.email,
        f"Email cannot be sent to { contact.email } from your alias { alias.email }",
        render(
            "transactional/bounce/bounce-email-reply-phase.txt",
            alias=alias,
            contact=contact,
            refused_email_url=refused_email_url,
        ),
        render(
            "transactional/bounce/bounce-email-reply-phase.html",
            alias=alias,
            contact=contact,
            refused_email_url=refused_email_url,
        ),
    )
    return status.E520


def handle_spam(
    contact: Contact,
    alias: Alias,
    msg: Message,
    user: User,
    mailbox: Mailbox,
    email_log: EmailLog,
    is_reply=False,  # whether the email is in forward or reply phase
):
    # Store the report & original email
    orig_msg = get_orig_message_from_spamassassin_report(msg)
    # generate a name for the email
    random_name = str(uuid.uuid4())

    full_report_path = f"spams/full-{random_name}.eml"
    s3.upload_email_from_bytesio(full_report_path, BytesIO(to_bytes(msg)), random_name)

    file_path = None
    if orig_msg:
        file_path = f"spams/{random_name}.eml"
        s3.upload_email_from_bytesio(
            file_path, BytesIO(to_bytes(orig_msg)), random_name
        )

    refused_email = RefusedEmail.create(
        path=file_path, full_report_path=full_report_path, user_id=user.id
    )
    db.session.flush()

    email_log.refused_email_id = refused_email.id
    db.session.commit()

    LOG.d("Create spam email %s", refused_email)

    refused_email_url = f"{URL}/dashboard/refused_email?highlight_id={email_log.id}"
    disable_alias_link = f"{URL}/dashboard/unsubscribe/{alias.id}"

    if is_reply:
        LOG.d(
            "Inform %s (%s) about spam email sent from alias %s to %s. %s",
            mailbox,
            user,
            alias,
            contact,
            refused_email,
        )
        send_email_with_rate_control(
            user,
            ALERT_SPAM_EMAIL,
            mailbox.email,
            f"Email from {alias.email} to {contact.website_email} is detected as spam",
            render(
                "transactional/spam-email-reply-phase.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
            render(
                "transactional/spam-email-reply-phase.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
        )
    else:
        # inform user
        LOG.d(
            "Inform %s (%s) about spam email sent by %s to alias %s",
            mailbox,
            user,
            contact,
            alias,
        )
        send_email_with_rate_control(
            user,
            ALERT_SPAM_EMAIL,
            mailbox.email,
            f"Email from {contact.website_email} to {alias.email} is detected as spam",
            render(
                "transactional/spam-email.txt",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
            render(
                "transactional/spam-email.html",
                alias=alias,
                website_email=contact.website_email,
                disable_alias_link=disable_alias_link,
                refused_email_url=refused_email_url,
            ),
        )


def handle_unsubscribe(envelope: Envelope, msg: Message) -> str:
    """return the SMTP status"""
    # format: alias_id:
    subject = msg["Subject"]
    try:
        # subject has the format {alias.id}=
        if subject.endswith("="):
            alias_id = int(subject[:-1])
        # {user.id}*
        elif subject.endswith("*"):
            user_id = int(subject[:-1])
            return handle_unsubscribe_user(user_id, envelope.mail_from)
        # some email providers might strip off the = suffix
        else:
            alias_id = int(subject)

        alias = Alias.get(alias_id)
    except Exception:
        LOG.w("Cannot parse alias from subject %s", msg["Subject"])
        return status.E507

    if not alias:
        LOG.w("No such alias %s", alias_id)
        return status.E508

    # This sender cannot unsubscribe
    mail_from = envelope.mail_from
    # Only alias's owning mailbox can send the unsubscribe request
    mailbox = get_mailbox_from_mail_from(mail_from, alias)
    if not mailbox:
        LOG.d("%s cannot disable alias %s", envelope.mail_from, alias)
        return status.E509

    # Sender is owner of this alias
    alias.enabled = False
    db.session.commit()
    user = alias.user

    enable_alias_url = URL + f"/dashboard/?highlight_alias_id={alias.id}"
    for mailbox in alias.mailboxes:
        send_email(
            mailbox.email,
            f"Alias {alias.email} has been disabled successfully",
            render(
                "transactional/unsubscribe-disable-alias.txt",
                user=user,
                alias=alias.email,
                enable_alias_url=enable_alias_url,
            ),
            render(
                "transactional/unsubscribe-disable-alias.html",
                user=user,
                alias=alias.email,
                enable_alias_url=enable_alias_url,
            ),
        )

    return status.E202


def handle_unsubscribe_user(user_id: int, mail_from: str) -> str:
    """return the SMTP status"""
    user = User.get(user_id)
    if not user:
        LOG.exception("No such user %s %s", user_id, mail_from)
        return status.E510

    if mail_from != user.email:
        LOG.exception("Unauthorized mail_from %s %s", user, mail_from)
        return status.E511

    user.notification = False
    db.session.commit()

    send_email(
        user.email,
        "You have been unsubscribed from SimpleLogin newsletter",
        render(
            "transactional/unsubscribe-newsletter.txt",
            user=user,
        ),
        render(
            "transactional/unsubscribe-newsletter.html",
            user=user,
        ),
    )

    return status.E202


def handle_transactional_bounce(envelope: Envelope, rcpt_to):
    LOG.d("handle transactional bounce sent to %s", rcpt_to)

    # parse the TransactionalEmail
    transactional_id = parse_id_from_bounce(rcpt_to)
    transactional = TransactionalEmail.get(transactional_id)

    # a transaction might have been deleted in delete_logs()
    if transactional:
        LOG.i("Create bounce for %s", transactional.email)
        Bounce.create(email=transactional.email, commit=True)


def handle_bounce(envelope, email_log: EmailLog, msg: Message) -> str:
    """
    Return SMTP status, e.g. "500 Error"
    """

    if not email_log:
        LOG.w("No such email log")
        return status.E512

    contact: Contact = email_log.contact
    alias = contact.alias
    LOG.d(
        "handle bounce for %s, phase=%s, contact=%s, alias=%s",
        email_log,
        email_log.get_phase(),
        contact,
        alias,
    )

    if email_log.is_reply:
        content_type = msg.get_content_type().lower()

        if content_type != "multipart/report" or envelope.mail_from != "<>":
            # forward the email again to the alias
            LOG.i(
                "Handle auto reply %s %s",
                content_type,
                envelope.mail_from,
            )

            contact: Contact = email_log.contact
            alias = contact.alias

            email_log.auto_replied = True
            db.session.commit()

            # replace the BOUNCE_EMAIL by alias in To field
            add_or_replace_header(msg, "To", alias.email)
            envelope.rcpt_tos = [alias.email]

            # same as handle()
            # result of all deliveries
            # each element is a couple of whether the delivery is successful and the smtp status
            res: [(bool, str)] = []

            for is_delivered, smtp_status in handle_forward(envelope, msg, alias.email):
                res.append((is_delivered, smtp_status))

            for (is_success, smtp_status) in res:
                # Consider all deliveries successful if 1 delivery is successful
                if is_success:
                    return smtp_status

            # Failed delivery for all, return the first failure
            return res[0][1]

        return handle_bounce_reply_phase(envelope, msg, email_log)
    else:  # forward phase
        handle_bounce_forward_phase(msg, email_log)
        return status.E513


def should_ignore(mail_from: str, rcpt_tos: List[str]) -> bool:
    if len(rcpt_tos) != 1:
        return False

    rcpt_to = rcpt_tos[0]
    if IgnoredEmail.get_by(mail_from=mail_from, rcpt_to=rcpt_to):
        return True

    return False


def handle(envelope: Envelope) -> str:
    """Return SMTP status"""

    # sanitize mail_from, rcpt_tos
    mail_from = sanitize_email(envelope.mail_from)
    rcpt_tos = [sanitize_email(rcpt_to) for rcpt_to in envelope.rcpt_tos]
    envelope.mail_from = mail_from
    envelope.rcpt_tos = rcpt_tos

    msg = email.message_from_bytes(envelope.original_content)
    postfix_queue_id = get_queue_id(msg)
    if postfix_queue_id:
        set_message_id(postfix_queue_id)
    else:
        LOG.w("Cannot parse Postfix queue ID from %s", msg["Received"])

    if should_ignore(mail_from, rcpt_tos):
        LOG.w("Ignore email mail_from=%s rcpt_to=%s", mail_from, rcpt_tos)
        return status.E204

    # sanitize email headers
    sanitize_header(msg, "from")
    sanitize_header(msg, "to")
    sanitize_header(msg, "cc")
    sanitize_header(msg, "reply-to")

    LOG.d(
        "==>> Handle mail_from:%s, rcpt_tos:%s, header_from:%s, header_to:%s, "
        "cc:%s, reply-to:%s, mail_options:%s, rcpt_options:%s",
        mail_from,
        rcpt_tos,
        msg["From"],
        msg["To"],
        msg["Cc"],
        msg["Reply-To"],
        envelope.mail_options,
        envelope.rcpt_options,
    )

    contact = Contact.get_by(reply_email=mail_from)
    if contact:
        LOG.e(
            "email can't be sent from a reverse-alias alias:%s, contact email:%s",
            contact.alias,
            contact.website_email,
        )
        return status.E203

    # unsubscribe request
    if UNSUBSCRIBER and rcpt_tos == [UNSUBSCRIBER]:
        LOG.d("Handle unsubscribe request from %s", mail_from)
        return handle_unsubscribe(envelope, msg)

    # emails sent to sender. Probably bounce emails
    if (
        len(rcpt_tos) == 1
        and rcpt_tos[0].startswith(TRANSACTIONAL_BOUNCE_PREFIX)
        and rcpt_tos[0].endswith(TRANSACTIONAL_BOUNCE_SUFFIX)
    ):
        LOG.d("Handle email sent to sender from %s", mail_from)
        handle_transactional_bounce(envelope, rcpt_tos[0])
        return status.E205

    # Handle bounce
    if (
        len(rcpt_tos) == 1
        and rcpt_tos[0].startswith(BOUNCE_PREFIX)
        and rcpt_tos[0].endswith(BOUNCE_SUFFIX)
    ):
        email_log_id = parse_id_from_bounce(rcpt_tos[0])
        email_log = EmailLog.get(email_log_id)
        return handle_bounce(envelope, email_log, msg)

    if len(rcpt_tos) == 1 and rcpt_tos[0].startswith(
        f"{BOUNCE_PREFIX_FOR_REPLY_PHASE}+"
    ):
        email_log_id = parse_id_from_bounce(rcpt_tos[0])
        email_log = EmailLog.get(email_log_id)
        return handle_bounce(envelope, email_log, msg)

    # iCloud returns the bounce with mail_from=bounce+{email_log_id}+@simplelogin.co, rcpt_to=alias
    if (
        len(rcpt_tos) == 1
        and mail_from.startswith(BOUNCE_PREFIX)
        and mail_from.endswith(BOUNCE_SUFFIX)
    ):
        email_log_id = parse_id_from_bounce(mail_from)
        email_log = EmailLog.get(email_log_id)
        alias = Alias.get_by(email=rcpt_tos[0])
        LOG.w(
            "iCloud bounces %s %s msg=%s",
            email_log,
            alias,
            msg.as_string(),
        )
        return handle_bounce(envelope, email_log, msg)

    if rate_limited(mail_from, rcpt_tos):
        LOG.w("Rate Limiting applied for mail_from:%s rcpt_tos:%s", mail_from, rcpt_tos)
        if should_ignore_bounce(envelope.mail_from):
            return status.E207
        else:
            return status.E522

    # Handle "out of office" auto notice. An automatic response is sent for every forwarded email
    # todo: remove logging
    if len(rcpt_tos) == 1 and is_reply_email(rcpt_tos[0]) and mail_from == "<>":
        LOG.w(
            "out-of-office email to reverse alias %s. %s", rcpt_tos[0], msg.as_string()
        )
        return status.E206

    # result of all deliveries
    # each element is a couple of whether the delivery is successful and the smtp status
    res: [(bool, str)] = []

    nb_rcpt_tos = len(rcpt_tos)
    for rcpt_index, rcpt_to in enumerate(rcpt_tos):
        if rcpt_to == NOREPLY:
            LOG.e("email sent to noreply address from %s", mail_from)
            return status.E514

        # create a copy of msg for each recipient except the last one
        # as copy() is a slow function
        if rcpt_index < nb_rcpt_tos - 1:
            LOG.d("copy message for rcpt %s", rcpt_to)
            copy_msg = copy(msg)
        else:
            copy_msg = msg

        # Reply case
        # recipient starts with "reply+" or "ra+" (ra=reverse-alias) prefix
        if is_reply_email(rcpt_to):
            LOG.d("Reply phase %s(%s) -> %s", mail_from, copy_msg["From"], rcpt_to)
            is_delivered, smtp_status = handle_reply(envelope, copy_msg, rcpt_to)
            res.append((is_delivered, smtp_status))
        else:  # Forward case
            LOG.d(
                "Forward phase %s(%s) -> %s",
                mail_from,
                copy_msg["From"],
                rcpt_to,
            )
            for is_delivered, smtp_status in handle_forward(
                envelope, copy_msg, rcpt_to
            ):
                res.append((is_delivered, smtp_status))

    for (is_success, smtp_status) in res:
        # Consider all deliveries successful if 1 delivery is successful
        if is_success:
            return smtp_status

    # Failed delivery for all, return the first failure
    return res[0][1]


class MailHandler:
    async def handle_DATA(self, server, session, envelope: Envelope):
        try:
            ret = self._handle(envelope)
            return ret
        except Exception:
            LOG.e(
                "email handling fail %s -> %s",
                envelope.mail_from,
                envelope.rcpt_tos,
            )
            return status.E404

    @newrelic.agent.background_task(application=newrelic_app)
    def _handle(self, envelope: Envelope):
        start = time.time()

        # generate a different message_id to keep track of an email lifecycle
        message_id = str(uuid.uuid4())
        set_message_id(message_id)

        LOG.i(
            "===>> New message, mail from %s, rctp tos %s ",
            envelope.mail_from,
            envelope.rcpt_tos,
        )

        app = new_app()
        with app.app_context():
            ret = handle(envelope)
            elapsed = time.time() - start
            LOG.i(
                "Finish mail from %s, rctp tos %s, takes %s seconds <<===",
                envelope.mail_from,
                envelope.rcpt_tos,
                elapsed,
            )
            newrelic.agent.record_custom_metric(
                "Custom/email_handler_time", elapsed, newrelic_app
            )
            return ret


def main(port: int):
    """Use aiosmtpd Controller"""
    controller = Controller(MailHandler(), hostname="0.0.0.0", port=port)

    controller.start()
    LOG.d("Start mail controller %s %s", controller.hostname, controller.port)

    if LOAD_PGP_EMAIL_HANDLER:
        LOG.w("LOAD PGP keys")
        app = create_app()
        with app.app_context():
            load_pgp_public_keys()

    while True:
        time.sleep(2)


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "-p", "--port", help="SMTP port to listen for", type=int, default=20381
    )
    args = parser.parse_args()

    LOG.i("Listen for port %s", args.port)
    main(port=args.port)