Chris Harms wrote: > We are having some trouble with our servers sending out backscatter > spam. I realize this is really a Sendmail issue, but if any list > readers have some insights on the best way to make Sendmail stop sending > bounces to outside domains, it would be greatly appreciated. The general approach is that you need to decide if a message is spam or not *during* the SMTP dialog. In that case, you can return a 5xx error code to the sending server directly. If you decide the message is spam after you've accepted it your only alternatives are to return a bounce-o-gram is to the sender address which as you've found is almost invariably forged, or to drop the message in the bit-bucket, which is counter to the letter of the SMTP standards and does nothing to indicate to the spammers that they should give up and go and do something more worthwhile. Sendmail's milter interface allows you to filter messages through AV and anti-spam filters -- FEATURE(`delay_checks') in your sendmail.mc file is often useful in that case. See http://www.sendmail.org/m4/anti_spam.html Some milters I use: spamass-milter: http://savannah.nongnu.org/projects/spamass-milt/ milter-greylist: http://hcpnet.free.fr/milter-greylist/ clamav-milter: http://www.clamav.net/ FEATURE(greet_pause) in sendmail.mc is also good at weeding out botnet style mailers. There's an excellent write up (of a pretty severe spam-filtering setup) which does a good job of exploring all the various issues at: http://www.acme.com/mail_filtering/ Cheers, Matthew -- Dr Matthew Seaman The Bunker, Ash Radar Station PGP: 0x60AE908C on servers Marshborough Rd Tel: +44 1304 814800 Sandwich Fax: +44 1304 814899 Kent, CT13 0PL, UK
Attachment:
signature.asc
Description: OpenPGP digital signature
---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
