I have mailman set up to send mail via an external MTA, which is supported by mailman and described in the documentation here: https://docs.mailman3.org/projects/mailman/en/latest/src/mailman/docs/mta.ht....
Specifically it says: |lmtp_host|and|lmtp_port|are parameters which are used by Mailman, but also will be passed to the MTA to identify the Mailman host. The “same host” case is special; some MTAs (including Postfix) do not recognize “localhost”, and need the numerical IP address. If they are on different hosts,|lmtp_host|should be set to the domain name or IP address of the Mailman host.|lmtp_port|is fairly arbitrary (there is no standard port for LMTP). Use any port convenient for your site. “8024” is as good as any, unless another service is using it.
However, there is a practical problem with LMTP (to receive incoming email) which is as follows:
The setup in mailman.cfg:
lmtp_host: lists.fast.za.net lmtp_port: 8024
Now, lists.fast.za.net is the mailman server. The docs say that mailman passes these on to the MTA. However, the MTA (postfix) on box2.gtahardware.co.za has the following setting in it main.cf:
virtual_transport=lmtp:[127.0.0.1]:10025
If I reply to a signup confirmation email for example, the mail is received and processed by box2.gtahardware.co.za, and it is not passed on to the mailman server.
So what is meant by "but also will be passed to the MTA to identify the Mailman host" in the docs?
If I change the config of the MTA (postfix) to be "virtual_transport=lmtp:[lists.fast.za.net]:8024", I assume the incoming mail will be forwarded, but how does postfix know that only the mailman emails should be forwarded and not all the other mail that the server at box2.gtahardware.co.za receives?
This is quite fuzzt to me at this stage. Could someone help me with some clarity please?