app/templates/emails/transactional/mailbox-invalid.txt.jinja2

{% extends "base.txt.jinja2" %}

{% block content %}
Your mailbox {{ mailbox.email }} and alias {{alias.email}} cannot have the same domain.

The alias domain should point to SimpleLogin servers so emails sent to it are forwarded by SimpleLogin.

The mailbox domain should be your "final" email address that can receive emails from SimpleLogin
    and cannot point to SimpleLogin.

Please either
- update the mailbox to a final email address on {{ mailbox_url }}
- remove {{alias.email}} domain from your custom domains
{% endblock %}