Debian – postfix: forward all mail sent to subdomain to other server

debianemailemail-serverpostfixsubdomain

I have a postfix mail server running on a Debian machine.

This server handles all incoming mail. However, I want all mail sent to a certain subdomain to be handled by another mail server running on another port on the computer.

In other words, all mail going to *@subdomain.domain.tld should go to address and port XX.XX.XX.XX:YYYY

At the moment I handle aliases in /etc/postfix/virtual but I don't see how to enter this rule there.

I should also mention, that postfix is (probably) not equipped to receive any mail coming to the subdomain at the moment. Therefore it would be great if you could explain how to get there from the start…

How can this be achieved?

Best Answer

If I understand your question correctly, you have to (1) enable relay for this domain and (2) set the destination server in transport map.

Backup the postfix config file before any changes (not required, but recommended).

In order to allow relay, you need to set relay_domains = subdomain.domain.tld in your postfix config (most likely /etc/postfix/main.cf).
Then, you need to set destination server in the config file for this domain using transport_maps = hash:/etc/postfix/transport (or any other file postfix has access to); create this file with content subdomain.domain.tld smtp:XX.XX.XX.XX:YYYY, (assign permissions if needed) and build the database using shell command postmap /etc/postfix/transport.

Don't forget to restart postfix after your changes.

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Proxy mail to different smtp server with Postfix

Postfix is extremely flexible (and therefore, complex) in its configuration, so there are various ways to achieve this. The simplest way would probably be to use a transport(5) table.

First, enable the use of a transport table in postfix:

/etc/postfix/main.cf:
    transport_maps = hash:/etc/postfix/transport

You'll also have to make sure that Postfix accepts mails for the addresses that will be handled by Lamson. Have a look at permit_auth_destination for the rules Postfix will apply to determine valid recipient addresses. For the following example, assuming "example.com" is a domain not otherwise known to Postfix, it's probably easiest to simply add it as relay domain:

/etc/postfix/main.cf:
    relay_domains = example.com

Then, create an appropriate table. E.g. to redirect all mail for the domain "example.com" as well as mail for "user@mydomain.org" to your local Lamson listening at port 10025:

/etc/postfix/transport:
    example.com          smtp:127.0.0.1:10025
    user@mydomain.org    smtp:127.0.0.1:10025

After that (and then once after every update to the transport table file) don't forget to run:

$ postmap /etc/postfix/transport

This should get you going. Be sure to read the transport(5) man page, which will give you more ideas on how to use this powerful facility.

Postfix rejects all incoming mail (Client host rejected: Access denied)

I think you need to put mydestination = mydomain.com in your config.

Next guess: We know the domain is right and that SASL works... so what I now suspect is that we're seeing an error in your restrictions. I'd start with recipient_restrictions and remove every rejection after permit_sasl_authenticated. If that works, add them back one at a time. If not, your next test is sender_restrictions.

Best Answer

Related Solutions

Proxy mail to different smtp server with Postfix

Postfix rejects all incoming mail (Client host rejected: Access denied)

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