The last parameter in the .qmail-default file tells vdelivermail what to do with non-matching emails. The default is to bounce the email back to the sender. But you can also delete it instead.
update your .qmail-default file from something like this:
| /home/vpopmail/bin/vdelivermail ” bounce-no-mailbox
to something like this:
| /home/vpopmail/bin/vdelivermail ” delete
