How can I configure Postfix to relay emails addressed to particular domains through a separate SMTP relay [duplicate]

Having some issues trying to get something working on postfix.

That is, I have a domain abc.com which is a destination domain on my postfix server 1.2.3.4, it hosts mailboxes for addresses in this domain locally by default - straight-forward.

However, I would like to be able to "relay" specific email addresses from within this same domain (say: [email protected]) to another postfix server [5.6.7.8]:2525 - yet still retaining the original ability of being able to deliver mail to all other addresses *@abc.com locally on my original postfix server 1.2.3.4.

Is anyone able to advise how I can go about doing this?

Thanks in advance!

Cont.

Thanks tater, I've actually gone with something similar so far, but still have one issue.

So I have transport file:

[email protected]  relay:[5.6.7.8]:2525
*@abc.com  local

And main.cf:

relay_domains = abc.com

This config sends to the relay perfect as I want, but any other addresses (in the wildcard scope) do not get delivered as they try to go straight back out the default relay server (another server altogether), where-as instead I'd like them to hit /etc/aliases or a local mailbox.

Solution 1:

One approach is to use transport maps. In main.cf, have a line like

transport_maps = hash:/etc/postfix/transport

and then in the transport file,

[email protected]  smtp:5.6.7.8:2525

This is searched in most- to least-specific order, so if you wanted to specify something else for abc.com you would do it like

[email protected]  smtp:5.6.7.8:2525
abc.com  smtp:1.2.3.4:25

but local transport is the default, so if that's what you want a second line is not needed.