@Mark & Stephen, now, where here everything appears to run smoothly on a new server, I want to change the testmail.domain (domain1) settings to mail.domain (domain2) settings.

It would be a great help, if this can be done by python script respectively a mailman3 shell script.

Is there any on your desk, or can you help me? I already defined in mailman/admin (django admin) that new target domain.

I guess, at the end, there might also be a very changes in mailman.cfg and settings.py necessary.