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Accepted
Max Muster
Asked: 2020-05-18 17:44:16 +0800 CST

POSTFIX how to use a relayserver just for a specific domain?

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I have two email servers: mx1.example.com (IMAP, SMTP) and mx2.example.com (SMTP gateway).

  • mx1.example.com is handling email for example.com, example.net and example.org.
  • mx2.example.com is configured as a gateway for mx1.example.com
    (I want him to send out all mails that originate from mx1.example.com)

Now I want to send the emails

  • from example.com and example.net via mx1.example.com normally
  • from example.org via mx1.example.com (password auth) to the gateway mx2.example.com (IP).

How can I configure this?

UPDATE: Please hurry up guys, the bounty expires in 2 days.

To be more clear: I know how to relay via mx2.example.com (how to send everything via mx2.) I just have to put the IP of mx2 in relayhost in the main.cf in mx1. But I want to make this selectively, just for example.org.

postfix

2 Answers

  1. Best Answer

    you cannot use transport as it is used to transport emails to the MAILBOX, you need to use

    sender_dependent_relayhost_maps

    it works like this in your main.cf:

    relayhost = mx1.example.org, mx2.example.org 
relay_domains = example.com, example.org, example.net

smtp_sender_dependent_authentication = yes
sender_dependent_relayhost_maps = hash:/etc/postfix/relaymap

    /etc/postfix/relaymap looks like this :

    @example.com    mx1.example.com
@example.net    mx1.example.com

@example.org    mx2.example.com
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  2. by using the selective relay feature:

    on mx1.example.com:

    • add a line : example.org smtp:mx2.example.com to /etc/postfix/transport

    • add a line : transport_maps = hash:/etc/postfix/transport to /etc/postfix/main.cf

    • run postmap /etc/postfix/transport
    • run postfix reload

    on mx2.example.com :

    • add mx1.example.com to mynetworks in /etc/postfix/main.cf

    • make sure you have something like:

      smtpd_relay_restrictions = permit_mynetworks, reject_unauth_destination in /etc/postfix/main.cf it is missing

    • run postfix reload

    Postfix to relay mails to other SMTP for particular domain

    http://www.postfix.org/STANDARD_CONFIGURATION_README.html

    http://www.postfix.org/SMTPD_ACCESS_README.html#lists

    https://xdeb.org/post/2017/12/20/mail-relay-mx-backup-and-spam-filtering-with-postfix/

    https://www.howtoforge.com/community/threads/postfix-relay-one-domain-to-smarthost-a-all-else-to-smarthost-b.62955/

    http://verchick.com/mecham/public_html/spam/relay_recipients.html

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