Stefan Bauer writes:
As i only use sqlite, i will give it a try to just copy the database files.
OK, if sqlite works for you, I think there's no hurry (I don't know of any severe performance issues for small sites, nor security issues).
However, I still recommend considering a migration to one of the more powerful RDMBSes like PostgreSQL or MySQL for the long run, because Mailman installations can easily scale to sizes where sqlite becomes a performance bottleneck. It's not that hard to do, because Mailman (mostly via the Django and SQLAlchemy ORMs, but I think there's some "raw" SQL in Mailman) sticks to the common core for SQL, so you can dump the database as SQL commands and then restore it in another SQL database without too much fiddling. You may need some fiddling, such as the database-specific initializations such as setting the encoding for text items and ensuring that sized columns are wide enough, but mostly that will be taken care of by the ORMs.
Regards, Steve