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Asked: 2016-04-02 17:54:20 +0800 CST

Postfix: SMTP Relay based on alias (from address)

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I recently noticed when I add an alias to a Gmail account they ask me for a remote SMTP server, username and password. Then, whenever I try to send an email using that alias it gets relayed by Gmail to the provided SMTP server.

Is there a way I can accomplish this setup on a Postfix install?

To clarify, on my server there's a virtual user [email protected] (with the aliases: [email protected] and [email protected]) if he sends an email:

  • With a from address of [email protected] => server will do the default delivery;
  • With a from address of [email protected] => server will relay email using smtp.xpto.com (with proper credentials);
  • With a from address of [email protected] => server will relay email using smtp.corpx.com (with proper credentials);

Ideally it would be nice If I could have a MySQL table with the external alises (for every virtual user) containing the external SMTP server domain, port, username and password. => This way I could setup a small web interface so my users could all their own external alises...

Thank you.

email

1 Answers

  1. Best Answer

    I guess you can achieve this by tuning the sender_dependent_default_transport_maps or sender_dependent_relayhost_maps Postfix parameters. For example:

    # /etc/postfix/main.cf
sender_dependent_default_transport_maps = hash:/etc/postfix/sender_maps.cf
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sender_credentials.cf
smtp_sasl_tls_security_options = noanonymous
smtp_sender_dependent_authentication = yes
smtp_tls_security_level = may

# /etc/postfix/sender_maps.cf
[email protected] smtp:[smtp.xpto.com]:587
[email protected] smtp:[smtp.corpx.com]

# /etc/postfix/sender_credentials.cf
[email protected] xptouser:xptopassword
[email protected] corpxuser:corpxpassword

    This example uses static hash tables. If your Postfix installation supports mysql_table(5), you can use MySQL queries instead.

    I am unable to test this solution now. I hope it works.

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