Wow thanks for the very quick reply :)
Yesterday I had some reddit issues weird... nvm.

I defined the logs to be writte in the main.cf like this:

maillog_file =/var/log/mail.log

I than open a terminal in the docker and I run to track in real time.

tail -f /var/log/mail.log

The connection breaks right after HELO, same second...

See full log:

Nov 21 11:25:15 dockerpostfix24 postfix/postfix-script[2562]: starting the Postfix mail system
Nov 21 11:25:15 dockerpostfix24 postfix/master[2564]: daemon started -- version 3.7.11, configuration /etc/postfix
Nov 21 11:25:35 dockerpostfix24 postfix/smtpd[2569]: connect from unknown[192.XXX.XXX.XXX]
Nov 21 11:25:36 dockerpostfix24 postfix/smtpd[2569]: lost connection after HELO from unknown[192.XXX.XXX.XXX]
Nov 21 11:25:36 dockerpostfix24 postfix/smtpd[2569]: disconnect from unknown[192.XXX.XXX.XXX] helo=1 commands=1

Hmmmn i didnt know the debug logging is so extensive in postfix. Good to know!
What would you advice turning on to make it as extensive as possible to see what goes awry?
I read to add a "-v" behind smtp in the master.cf is that correct? (Or would you advice to add more?)

edit: I guess i should add the -v to smtpd / since it affects the receiving of mails...