If you have too many mails/spams tend to pending moderator requests in mailman queue it can be removed by:
$ cd ~mailman
$ bin/discard /var/lib/mailman/data/heldmsg--*
And if the no. of argument list exceeds you can try:
$ find /var/lib/mailman/data -name heldmsg--\* -print | xargs bin/discard
* the path of mailman depends on your implementation anyway.