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Email from docker container dropped by host

Hi all,
I have an app (4Minitz) that I’m running through Docker
I had everything running perfectly and I had a major server crash. I didn’t loose anything per say but the easiest thing to do to recover was to simply create a new VPS server instance and move everything over. The old and new server instance should be almost identical. Exim config is the same as is the control panel I use (Hestia).

The issue I’m now having is that the Docker instance of 4Minitz cannot send mail via Exim on the host. The first error is that Docker (via the 4Minitz app) is trying to send mail as an IP address instead of a FDN. Exim dislikes that. The second error is “TLS did not properly terminated”.
I’ve tried running the instance using the -net host switch. Exim still complains.
I can send mail from mail clients and I receive mail with no problems. The strange thing is that the server config is exactly (as best as I can tell) the same as before). I’ve asked the question to the 4Minitz guys as well as the Hestia control panel forum. No-one seems to be able to figure this out. I’m using Docker for this App because it’s Java and that is not in my wheelhouse.

Thanks. I do appreciate any suggestions you folks might have.

I was able to resolve this issue by port forwarding docker container port 25 to docker host.

Thanks but I have no idea how to do that. I’m a newbie.