OT: How do I stop this???

[Gerry Doris]

I know this is OT but you folks are the most knowledgeable and helpful
sendmail folks I know!

Someone has misconfigured their email client and is pumping out messed up
emails at the rate of one every 5 minutes.  Each of these is generating an
error message in my logs and a warning message to me!  I know how to turn
off the error messages but I can see where this could easily turn into a
DoS attack if someone was doing this intentionally and I'm interested in
knowing how to stop it.

I've tried to put the domain name and its ip in sendmail's access database
but that doesn't work.  I can't think of any other way to discard these
emails before they cause sendmail to start complaining.

Here's the actual errors...

Unusual System Events
=-=-=-=-=-=-=-=-=-=-=
Mar 27 12:15:05 tiger sendmail[24994]: i2RHF53U024994: Syntax error in mailbox
address "dayzersagency?@spinfinder.com" (non-printable character)
Mar 27 12:20:06 tiger sendmail[25157]: i2RHK63U025157: Syntax error in mailbox
address "dayzersagency?@spinfinder.com" (non-printable character)
Mar 27 12:25:07 tiger sendmail[25292]: i2RHP73U025292: Syntax error in mailbox
address "dayzersagency?@spinfinder.com" (non-printable character)

--
Gerry

"The lyfe so short, the craft so long to learne"  Chaucer