my server getting email bombs, HELP!!!

[kfliong]

<x-flowed>
Hi all,

My server is getting bomb by tons of emails. So bad that it make the load
of my server to go up to 15. Sometimes even more than 20. I found out that
we are getting lots of mails where the from is empty and the subject vary
as below :

Warning: could not send message for past 8 hours
Returned mail: see transcript for details
Undeliverable: Get that L.oan youve always wanted Hoyt
Delivery Status Notification (Failure)

all are undelivered mails send back to us but in the first place, we did
not sent them out. Someone is masking as our domain and sending out spams.
Cause the mails that get delivered back is sent to email accounts that does
not exist. Mailscanner is able to filter them but not fast enough as the
mails comes in splitseconds.

Anyway I can filter this at MTA level? Or can i set sendmail to reject
mails that have "blank" from field?

Urgent as my server is dying......Thanks in advance.

------------------------ MailScanner list ------------------------
To unsubscribe, email jiscmail at jiscmail.ac.uk with the words:
'leave mailscanner' in the body of the email.
Before posting, read the MAQ (http://www.mailscanner.biz/maq/) and
the archives (http://www.jiscmail.ac.uk/lists/mailscanner.html).
</x-flowed>