Ok, so after looking into open ports a bit more, it turns out that there is nothing listening on port 587. As such, there is no SMTP server running or listening to any port whatsoever. I figure that an SMTP server may only start running if I enable incoming emails (setting which was not enabled, purposefully). When I enabled incoming email setting, sudo netstat -tlnp | grep 587 was finally returning something and n8n configuration worked fine.
So to sum up, if my understanding is correct, when only using outbound mail, there isn't an actual SMTP server running, but only some kind of abstraction that containerized apps can use to send email directly through the mail relay (the internals of this are fuzzy to me...), so I need to enable incoming emails in order to send emails...
But I'm glad I was at least able to make this work before going into 2026. Thanks for the help and for putting me on the right path here.
Thank you for all the great work you do Cloudron Team, and wishing you all the best for the new year :).
