Ah okay well Postal only supports STARTTLS which I strongly suspect is different than the SSL/TLS option you have so I'd try putting Postal back on port 25 and then turning off the SSL/TLS option in your HPE to see what happens, hopefully you'll see more log lines and the message will actually get sent.

If HPE doesn't have support for STARTTLS then you won't be able to use a secure connection unfortunately.

try putting Postal back on port 25 and then turning off the SSL/TLS option in your HPE to see what happens

That’s what I tried initially, as you can see at the start of this discussion. I reverted the changes, but no luck. I also tested with a Postfix server using the same configuration: port 25, no SSL/TLS settings enabled, no credentials and it worked as expected. Switching back to Postal, it’s still not working.

And yes, HPE iLO should support STARTTLS.

I appreciate your help so far.

If you're definitely providing credentials to HPE then I'm not sure why it would cut off after receiving the list of capabilities.

If there are no further logs in the HPE side then you might have to use something like wireshark to see what is actually being sent by it and that would hopefully let you figure out why Postal isn't doing anything else with the connection.

Hi again and sorry for the long wait.

Just to make sure, by credentials you mean the one you can create in Postal, right? If so, yes, that's what I was providing.

Regarding the Wireshark logs, for me it looks like the same, as you can see in the postal SMTP logs, ending with:

SMTP 86 S: 250 postal.custom-domain.de

Are you able to read more into Wireshark logs? If yes, I can provide you the full output.

I think you have to figure out what HPE is doing instead of telling Postal which auth method it wants to use, if you have to read that from wireshark then hopefully its in plain text so you can see what is happening.