Handle undisclosed recipients header (#1314)

* remove TO header if it's set to "undisclosed-recipients:;"

more info on https://www.rfc-editor.org/rfc/rfc4356.txt

* remove unnecessary indentation character in plain text email

email_handler.py

@@ -1171,7 +1171,13 @@ def handle_reply(envelope, msg: Message, rcpt_to: str) -> (bool, str):
     add_or_replace_header(msg, headers.FROM, from_header)
 
     try:
-        replace_header_when_reply(msg, alias, headers.TO)
+        if str(msg[headers.TO]).lower() == "undisclosed-recipients:;":
+            # no need to replace TO header
+            LOG.d("email is sent in BCC mode")
+            del msg[headers.TO]
+        else:
+            replace_header_when_reply(msg, alias, headers.TO)
+
         replace_header_when_reply(msg, alias, headers.CC)
     except NonReverseAliasInReplyPhase as e:
         LOG.w("non reverse-alias in reply %s %s %s", e, contact, alias)

templates/emails/transactional/message-quarantine-dmarc.txt.jinja2

@@ -1,11 +1,11 @@
 {% extends "base.txt.jinja2" %}
 
 {% block content %}
-  An email from {{ from_header }} to {{ alias.email }} is put into Quarantine as it fails anti-phishing check.
+An email from {{ from_header }} to {{ alias.email }} is put into Quarantine as it fails anti-phishing check.
 
 
-  You can view the email at {{ refused_email_url }}.
-  This email is automatically deleted in 7 days.
+You can view the email at {{ refused_email_url }}.
+This email is automatically deleted in 7 days.
 
-  More info about the anti-phishing measure on https://simplelogin.io/docs/getting-started/anti-phishing/
+More info about the anti-phishing measure on https://simplelogin.io/docs/getting-started/anti-phishing/
 {% endblock %}

templates/emails/transactional/non-reverse-alias-reply-phase.txt.jinja2

@@ -1,19 +1,19 @@
 {% extends "base.txt.jinja2" %}
 
 {% block content %}
-  Hi
+Hi
 
-  Your email sent to {{ destination }} from {{ alias }} ({{ subject }}) contains an address
-  which isn't a reverse-alias in the To: or Cc: field.
+Your email sent to {{ destination }} from {{ alias }} ({{ subject }}) contains an address
+which isn't a reverse-alias in the To: or Cc: field.
 
-  The email was then directly sent to this recipient and doesn't pass by SimpleLogin.
-  Unfortunately, it reveals your real mailbox address to the recipient.
-  Please create a reverse alias for each recipient to make sure your mailbox stays hidden and re-send the email.
+The email was then directly sent to this recipient and doesn't pass by SimpleLogin.
+Unfortunately, it reveals your real mailbox address to the recipient.
+Please create a reverse alias for each recipient to make sure your mailbox stays hidden and re-send the email.
 
-  In case some reverse aliases are also present in To: or Cc:, SimpleLogin won't deliver this email to the
-  corresponding contacts to avoid any potential side effect. Please remove the non reverse-alias addresses and
-  re-send the email.
+In case some reverse aliases are also present in To: or Cc:, SimpleLogin won't deliver this email to the
+corresponding contacts to avoid any potential side effect. Please remove the non reverse-alias addresses and
+re-send the email.
 
-  More info about reverse-alias can be found on https://simplelogin.io/docs/getting-started/reverse-alias/
-  and how to send an email from your alias on https://simplelogin.io/docs/getting-started/send-email/
+More info about reverse-alias can be found on https://simplelogin.io/docs/getting-started/reverse-alias/
+and how to send an email from your alias on https://simplelogin.io/docs/getting-started/send-email/
 {% endblock %}

templates/emails/transactional/noreply.text.jinja2

@@ -1,6 +1,8 @@
 Hi!
 
-Thanks for getting in touch. This mailbox cannot receive any emails. If you need help, please go to https://app.simplelogin.io/dashboard/support to contact us.
+Thanks for getting in touch. This mailbox cannot receive any emails.
+
+If you need help, please go to https://app.simplelogin.io/dashboard/support to contact us.
 
 Best!
 SimpleLogin team

templates/emails/transactional/spoof-reply.txt.jinja2

@@ -1,10 +1,10 @@
 {% extends "base.txt.jinja2" %}
 
 {% block content %}
-  Unauthorized attempt to send an email to {{ contact.email }} from your alias {{ alias.email }} using
-  {{ sender }} has been blocked.
+Unauthorized attempt to send an email to {{ contact.email }} from your alias {{ alias.email }} using
+{{ sender }} has been blocked.
 
-  To protect against email spoofing, only your mailbox can send emails on behalf of your alias.
-  SimpleLogin also refuses emails that claim to come from your mailbox but fail DMARC.
+To protect against email spoofing, only your mailbox can send emails on behalf of your alias.
+SimpleLogin also refuses emails that claim to come from your mailbox but fail DMARC.
 {% endblock %}