removing 'dead' messages

i have a user (using exchange) who had his configuration set
to keep 
messages on the server after delivery.  he never deletes
anything, and 
as a result, has messages in his mdir dating back to 2005.

i happened to discover this by accident and he has now
changed his 
configuration so that mail is deleted after delivery.

the question is, how do i get rid of all those old messages
sitting on 
the server? if i just delete them manually, is there
anything else i 
need to touch?

david camm
advanced web systems
keller, tx