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Spam affects us in two ways:

  • Spam to public contact addresses, such as webmaster@, listmaster@, chairman@, list owners, etc.
    • Tends to overload anyone monitoring such aliases
    • Might cause liberty to be flagged as a spam-source if forwarded off-system
    • Causes spam backscatter problems
  • Spam to mailing list posting addresses
    • Clogs the non-member-posting hold queue
    • Forces us to silently discard all non-member postings

Currently, we have little to nothing in the way of sophisticated spam-filtering. Something better would be nice. We should look at doing things both in the MTA and in Mailman.

General techniques

  • It should be possible to have the MTA check to see if a post to a mailing list address is from a subscriber, and if not, reject said message during the SMTP transaction. That would be a huge benefit, I think.
  • RBLs
    • Someone else does the bulk of the work -- BruceDawson - 22 Feb 2006
    • Have a small footprint on the system -- BruceDawson - 22 Feb 2006
    • Catch 90% of the SPAM. -- BruceDawson - 22 Feb 2006
    • The lists are maintained by others -- BruceDawson - 22 Feb 2006
    • Some discriminate against dynamic and other large block of IPs. -- BruceDawson - 22 Feb 2006

Specific software

  • MailScanner
    • Easy to configure, modify configuration, very flexible. Auto-updates for ClamAV, RulesDuJour. Integrates SpamAssassin without separate daemon. Disarms spam, phishing, viruses, "active" HTML mail. Somewhat CPU intensive. I've never seen decent hardware CPU bound by it though. -- BillMcGonigle - 20 Feb 2006
    • Bill, what's "decent hardware"? -- BenScott - 15 Oct 2006
  • SpamAssassin
    • Easily configured, low maintenance, good results, low-to-zero false-positives. -- MikeLedoux - 21 Feb 2006

Discarding non-member list mail

We can solve the spam problem for mailing lists completely and easily by simply discarding (or better yet, rejecting during the SMTP conversation) all mail from non-list-members. After taking care of the mailman admin approval queues for a few months, I don't see this as being a problem. We get so little legit mail in these queues that I think I'm willing to call the once-every-other-month mis-posted message "acceptable losses". That would kill the gnhlug-jobs list, though. OTOH, that list doesn't appear to get any legit traffic, so maybe it's already dead. A web-based interface would be better anyway, I think. -- BenScott - 23 Feb 2006

The gnhlug-jobs list does get some legit traffic. We have had 9 legit messages so far in February, mixed in with over 100 garbage messages. I am not sure the list is worth keeping in current form, though, the high volume of spam is a PITA. -- MikeLedoux - 23 Feb 2006

Since the above discussion took place, Mailman was configured to silently discard all mail from addresses not subscribed to the list. The spam volume was too high to do otherwise, and we lacked a better solution. This has been in place for quite some time now. -- BenScott - 21 Aug 2007

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