Postfix and antispamming

[BeNe]

Source --> http://www.policyd-weight.org/

Quote:policyd-weight is a Perl policy daemon for the Postfix MTA (2.1 and later) intended to eliminate forged envelope senders and HELOs (i.e. in bogus mails). It allows you to score DNSBLs (RBL/RHSBL), HELO, MAIL FROM and client IP addresses before any queuing is done. It allows you to REJECT messages which have a score higher than allowed, providing improved blocking of spam and virus mails. policyd-weight caches the most frequent client/sender combinations (SPAM as well as HAM) to reduce the number of DNS queries.

After the first three SMTP commands (HELO, MAIL FROM: and RCPT TO the client's IP address, corresponding DNS records (A, MX and PTR) and multiple DNSBLs can be checked, verified and scored. If the client tries to forge headers or supplies non-existent DNS or bogus data the spam score will increase, even more so if the client is listed in one or more DNSBLs. Such mails can be rejected while in transfer, before the mail body is received by your MTA. This is different from SpamAssassin or amavisd-new: for scoring or filtering with these programs, mail needs to be accepted and queued, bandwidth is used, CPU-time is wasted and mail cannot be rejected without creating a bounce. Please have a look at the graphical working scheme.

Postfix' built-in checks can be too tough for poorly configured clients: one hit, and the mail gets rejected. policyd-weight is designed to be fair (DynDNS MX users get through if their MTA is setup properly, even if their ISP net is DUL-listed), because its decision whether to reject or accept a mail is based on multiple factors.

Of course you should still have SpamAssassin and Clamav running (especially if you are responsible for a company's security and data). But these programs will have a lot less to do and thus decrease the need for bandwidth and CPU cycles. Also you might not need greylisting (which would make sense for users that receive a lot of new spam, though), SPF, extraordinary whitelists or SQL and other DBs anymore

Greez BeNe