[vchkpw] Deny on bad username?

[Dave Richardson - Lists]

I've seen prior references on this list to a patch/script that will deny 
incoming SMTP when the username/account is unknown.  After getting a ton 
of crap from the SoBIG virus (and various spam probes) I would really 
like to consider adding this to my system.  My implementation is the 
following:

qmail 1.03 with many common patches, including QMAILQUEUE.
courier-imap (1.4?)
vpopmail 5.2.1
Squirrelmail 1.4
MySQL support for both vpopmail and squirrelmail
Spamassassin and CLAM AV
That might be too much detail, but I wondered if the MySQL support would 
be an issue.  
Please link me to wherever I can find a description of this SMTP denial 
support.
Thanks, Dave.