Dear community,
I’ve just set up mailcow on a public server and it’s working fine. Only issue left is handling of (service) mails coming from my home lab (non-public-domain fritz.box). I have Nullmailer installed as MTA on internal hosts and they use a “systems” mailbox on mailcow to send mails to hostmaster@example.com.
However, sending out an actual message does not work, the mail.log writes:
nullmailer-send[663]: From: <root@host.fritz.box> to: <hostmaster@example.com>
nullmailer-send[663]: Message-Id: <1636087318.835751.3479756.nullmailer@host.fritz.box>
nullmailer-send[3479758]: smtp: Failed: 553 5.7.1 <root@host.fritz.box>: Sender address rejected: not owned by user systems@example.com
What’s “funny”, though is, that the automatically generated bounce message is accepted by mailcow for delivery:
nullmailer-send[663]: From: <> to: <hostmaster@example.com>
nullmailer-send[663]: Message-Id: <1636087322.532757.3479771.nullmailer@host.fritz.box>
nullmailer-send[3479772]: smtp: Succeeded: 250 2.0.0 Ok: queued as EDB5E81291
How can I fix this, without turning mailcow into an open relay?
Cheers,
m0wlheld