How to delete lots of mails

Due to a ping-pong situation cased by a users vacation message I have some 30000+ mails in queue for delivery. If I try to delete those in Server Admin the whole server crashes and reboots. If I try to turn virus and spam control off to have the shit delivered as fast as possible I get this error message: postfix/qmgr[514]: warning: connect to transport smtp-amavis: Connection refused and nothing gets passed. My server is an old G4 so spam and virus control take som time... Any hints how to solve this?