For those of us that feel strongly that email should be a reliable transport medium.

Kevin Spicer kevins at BMRB.CO.UK
Tue Feb 10 23:33:45 GMT 2004

On Tue, 2004-02-10 at 20:56, Julian Field wrote:
> But in the meantime, does anyone have any good ideas for a happy medium,
> such as enabling it but not documenting it, or producing a nasty log
> message if it is used, or something like that?
> All constructive ideas are most welcome.
Personally I'm happy to see it left off - but in the interests of
debate, four points (1 long 3 short)

First point...
There are a number of spamassassin tests that spot mail with forged
headers (maybe not all of them - but a fair few).  The introduction of
SPF support in SA2.70 should also help with spotting some forged mail
(especially if AOL continue to use it) [I don't want to get into another
debate about the merits or otherwise of SPF - but can we agree for sites
that choose to use SPF it should be a useful indicator for modifying
SpamAssassin scores...]

Simply checking for the presence of these indicators (or even the total
score contributed by those tests) in the spamassassin report would help
to determine whether a source is probably spoofed. Then the bounce
option could only be applied to those that are not obviously false.

Additionally the  triggering of DCC or pyzor tests is also a good
suggestion of whether it is worthwhile bouncing a mail.

I'm not sure offhand exactly what tests SA does, but some obvious ideas
spring to mind, which could perhaps be implemented in SA rules.//

The mail originates from one of the 'senders' MX's  (good indicator that
the domain at least is likely not forged - unless its an open relay!)
The mail originates from a host in the same class C as one of the
'senders' MX's
A reverse lookup on the senders IP gives a hostname in the same domain.

NOTE that I'm not saying that any of these are hard and fast indicators
or forged addresses (they all have flaws) but as part of a spamassassin
ruleset they may be helpful.
Certainly where spamassassin detects that headers are forged there is no
excuse for bouncing the mail(?)

Second point - Admins who do bounce mail should - at the very least -
ensure that the mail they wish to bounce was originally addressed to a
valid user.  I'll be posting something to the FAQ soon describing a
method of doing this for those using sendmail to relay to exhange.

Third (contentious) point - Of course this is one benefit of a milter
(but lets not start that debate!), I choose not to use a milter, but
then I don't bounce spam.

Fourth (really contentious) point - Maybe its about time someone started
an RBL for mindless autoresponders?



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