amavisd-new 2.7.1 , dkim-adsp=pass

Mark Martinec Mark.Martinec+amavis at
Wed May 23 18:39:02 CEST 2012


> While having your attention, might I ask you another DKIM related question?
> What happens if a sender has DKIM and has signed his/her subject line?
> Does amavis take care of that or will it prefix the subject with SPAM/Not
> Checked/etc entries and break DKIM?

If you have it configured to modify a Subject, it will do so regardless
of whether this header field was signed or not. And yes, this will break
subsequent DKIM tests, so it is prudent to tag a subject close to a final
delivery, where no further sw components will be re-examining the signature.

Note that Subject tagging is only done for local recipients, so outgoing
signed mail will not be affected.

> Well... I think we should not go into discussion about that but IMHO good
> written C code usually beats good written Perl code.

Stress on 'good'. Incidently, benchmarking of DKIM signature verification
in a perl module Mail::DKIM (as used by amavisd and SpamAssassin) revealed
that the pure-perl version can canonicalize a message and verify a signature
faster than Mail::OpenDKIM, which uses a C library of OpenDKIM underneath.
The reason is that the Perl implementation deals with large chunks of text
in one operation, where the OpenDKIM lost precious time in its chain of
subroutine calls, passing around small pieces of text.


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