Removing bogus bounced mail...

Hi!

I have some mail accounts on my mailserver, who forwards their emails to
another email address. I use a my ISP smarthost, whenever I want to send
mails because they are bloking port 25. Problem is some spammers are able to
send mail to some of my accounts without a return address e.g. "From: <>".

The message I get when they are bounced is:

"SMTP error from remote mailer after MAIL FROM:<>: host my.isp.com
[XXX.XXX.XXX.XXX]: 501 Syntax error in return path".


How do I make Exim delete _all_ mails where sender is "<>"? Becuse when some
of these spammails are sent to one of my accounts who forwards their emails
to another account, I will recieve those error mails, when they are bounced
from my ISP's smarthost.

AFAIK this will in some part conflict with RFC821.

Any help will be appreciated!

Lasse