Postfix/Suppress_backscatter_NDRs_from_spoofed_senders

From http://archives.neohapsis.com/archives/postfix/2010-01/0573.html

Maintaining state, so you can drop NDRs that arrive as a result of someone spoofing your domain/s.

What I'm doing is this:

• store a hash of From:, To: and Date: header of all outgoing mail
• accept all bounces that include From:, To: and Date: headers whose hash matches a stored hash
• remove stored hashes older than 4 days

This method does lead to rejection of valid bounces that don't include the above mentioned headers. However, I consider those bounces useless anyway.