I have QmAil installed on a CentOS5 machine and have been successfully using mailman for some time.
I upgraded my installation of PLESK to 9.0.1 which has stopped mailman from working as described elsewhere on the web.
The recommended fix is to insert a sym link to the mm_wrapper file which I have done using the commands:
ln -s /usr/lib64/plesk-9.0/mm_wrapper mm_wrapper
this link is created as expected.
Emails to mailing lists are still bounced with the message:
preline: fatal: unable to run /var/qmail/bin/mm_wrapper: file does not exist
I have tried restarting the service already.
Very keen to get this working!