[MM3-users] Getting connection refused on postfix trying to connect to mailman-core:lmtp

I've got a setup where postfix runs inside one VM(container) and mailman runs inside another one (maxking containers). I've wired everything according to docs yet I'm getting:

postfix/lmtp[266]: 66A72800A87: to=<somelist@lists.here.stanford.edu>, relay=none, delay=0.5, delays=0.48/0.01/0/0, dsn=4.4.1, status=deferred (connect to mailman-01.stanford.edu[1.2.3.4]:8024: Connection refused)

is it something I'm missing on mailman side or postfix side (like this post suggests: https://gitlab.com/mailman/mailman/issues/365 )?

Note: I've configured TLS on postfix side but none on mailman side. Is that the issue?

-- Sr System and DevOps Engineer SoM IRT