Login to qmailadmin as postmaster for your domain and click the set catchall deleted at the bottom of the email account menu, or edit ~vpopmail/domains/domain.com/.qmail-default to look like the following:

| /home/vpopmail/bin/vdelivermail '' bounce-no-mailbox

To discard double-bounces, follow these steps:

# echo yourdomain.tld > /var/qmail/control/doublebouncehost
# echo doublebounce > /var/qmail/control/doublebouncto
# echo "#" > ~vpopmail/domains/yourdomain.tld/.qmail-doublebounce
# qmailctl restart

This will tell qmail to deliver double-bounces to doublebounce@yourdomain.tld.

The "empty" (only has pound sign) .qmail-doublebounce file in that
domain's directory will tell qmail to deliver the message to nowhere.
Now you will no longer be bombarded with useless double bounces.

Enjoy the quiet. :)