[Mimedefang] SPF Usefulness (was Re: SNARE spam detection)

Kelson kelson at speed.net
Wed Jul 29 20:49:31 EDT 2009

- wrote:
> It's useful as a message REJECTION tool.  It can also useful when the
> method passes, in that we have a responsible IP address to complain
> to or about.

SPF and DKIM are also useful as one component of whitelist data, because 
an SPF pass means you can trust the envelope sender's domain name.

For example:
1. You want to whitelist mail that's definitely from example.com.
2. example.com publishes an SPF record.
3. If you get mail that claims to be from example.com *and*
    passes SPF, you whitelist it.
4. If a message fails SPF for example.com, or passes SPF for another
    domain, just let it run through the normal filter path.

This is how SpamAssassin's whitelist_from_spf and whitelist_from_dkim 
methods work.  (Well, mostly.  It still runs through the regular 
filters, just subtracts a bunch of points at the end.)

Kelson Vibber
SpeedGate Communications <www.speed.net>

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