:-)
The message is delivered to a maildir store. I guess this is not a Mailman problem, but a Postfix one. Perhaps you got address rewriting wrong - is the mail really supposed to be delivered to kozlowsm@alpha.mini.pw.edu.pl with the local(8) delivery agent? After all, your mail address seems to be kozlowsm@mini.pw.edu.pl, without the "alpha" part - but I don't know your mail setup.
Normal mail sent to any of the followings:
kozlowsm@alpha.mini.pw.edu.pl M.Kozlowski@alpha.mini.pw.edu.pl kozlowsm@mini.pw.edu.pl M.Kozlowski@mini.pw.edu.pl
is delivered OK!
When using a content_filter, you should make sure that you only do virtual address rewriting once, i.e. either the main smtpd (or the one you use for injecting messages generated by Mailman) _or_ the smtpd used for reinjection from amavisd-new should have set "receive_override_options=no_address_mappings" - only one, not both of them, preferarbly the one used for reinjection from amavisd-new.
Could you explain more in detail?
Best reards, /M