[Mimedefang] recipient filter and rbl's

[Kimmo Jaskari]

On Fri, 2007-11-30 at 15:02 +0000, Paul Houselander wrote:

> My mailserver acts as a gateway to a few MS exchange systems and im using
> mimedefang to reject invalid recipients.

Why not use Sendmail for this too? It seems far more efficient to get
Sendmail to block invalid addresses as well as do the DNSBL check (and
then perhaps even do another DNSBL check in Mimedefang on the content of
the e-mail that gets that far; that combo is brilliantly effective in
blocking spam.)

I found a couple of great Perl scripts on the Mimedefang Wiki; they talk
LDAP to the Exchange servers, fetch a list of valid mail addresses and
then write those into the Sendmail access db. 

End result - sendmail rejects all non-valid addresses and rejects all
Spamhaus matches before they ever reach MD. The load on my gateways
dropped dramatically now that MD only has to process valid mail for
viruses and spam content. To make sure nothing outgoing is blocked I
have the Exchange server IP's specifically set to allow relaying for
those machines as a whole.

Adding DNSBL zen.spamhaus.org to my Sendmail was the best thing I've
ever done, spam-fighting wise. It's really uncanny how much Spam just
goes away when you start rejecting dial-us and dynamic DNS addresses,
and I have yet to get a single complaint about false positives.

/Kimmo