I did it with email aliases. I created an alias for each of the addresses and pipe the email to |/bin/true, essentially discarding it. With qmail, used on my server, you need a new file for each alias.
I used a PHP script via SSH shell in the /var/qmail/mailnames/lmhost2.com folder, where aliases are created:
#!/usr/bin/php
<?phpfor($i=0;$i<=11000;$i++){ exec("echo \"|/bin/true\" > .qmail-test$i");}?>
Of course, hard drive access becomes an issue with several thousand files in a folder and this may not be the best way to do it. I think .procmailrc, for example, could achieve this and more (ie. discard test*@lmhost2.com) in just a few lines. I should probably look into .procmailrc for qmail... :)
Regards