> We've got plenty of time, but I suggest not waiting until it becomes a
> big problem before desperately rushing to fix it.... :)
Depends on how one defines where a problem starts to become 'big'.
For me the problem of large messages was big enough early last year so
that I had to implement a solution for it in amavisd-new 2.6.3 - with
a corresponding support in the SpamAssassin 3.3.0 library (most of it
in its DKIM plugin, as mentioned by Michael).
From 2.6.3 release notes (April 22, 2009):
- large messages beyond $sa_mail_body_size_limit are now partially passed
to SpamAssassin and other spam scanners for checking: a copy passed to
a spam scanner is truncated near or slightly past the indicated limit.
Large messages are no longer given an almost free passage through spam
checks.
Note that message truncation can invalidate a DKIM or DK signature.
If using (non-default) SpamAssassin rules to assign score points to mail
with no valid signatures from authors which are expected to always provide
a valid signature, the message truncation can cause false positives on
these rules. As a workaround, to a truncated message passed to spam
scanners, amavisd inserts a header field:
X-Amavis-MessageSize: mmmmm, TRUNCATED to nnnnn
which can be captured by SpamAssassin rules, e.g.:
header __TRUNCATED X-Amavis-MessageSize =~ m{\A[^\n]*TRUNCATED}m
and used in rules like NOTVALID_EBAY to prevent them from triggering.
Starting with version 3.3.0 of SpamAssassin, its DKIM plugin understands
the issue and receives undamaged DKIM signature objects directly from
amavisd, so the above workaround is not needed. Also, a hit on a __TRUNCATED
rule is automatically generated (explicit header rule is not necessary),
just in case it might be useful for some purpose.
Just did a grep on our log, seeking out large spam messages (beyond 420 kB)
and print their sizes. Below is the complete list for March 2010. Seems we
are getting about 4.5 large spam messages daily on the average (out of
about 75k messages daily). A lot? Depends on one's point of view.
Mar 1 score: 12.7, size: 533 kB
Mar 1 score: 23.9, size: 435 kB
Mar 1 score: 16.4, size: 533 kB
Mar 1 score: 7.4, size: 490 kB
Mar 1 score: 9.1, size: 490 kB
Mar 1 score: 19.6, size: 721 kB
Mar 2 score: 15.1, size: 1132 kB
Mar 2 score: 16.9, size: 643 kB
Mar 2 score: 16.9, size: 643 kB
Mar 2 score: 7.3, size: 587 kB
Mar 2 score: 21.9, size: 721 kB
Mar 2 score: 21.6, size: 527 kB
Mar 2 score: 24.8, size: 436 kB
Mar 2 score: 20.5, size: 527 kB
Mar 2 score: 20.6, size: 528 kB
Mar 3 score: 23.6, size: 435 kB
Mar 3 score: 30.4, size: 543 kB
Mar 3 score: 30.2, size: 543 kB
Mar 3 score: 30.2, size: 543 kB
Mar 3 score: 31.5, size: 543 kB
Mar 3 score: 18.3, size: 1132 kB
Mar 3 score: 31.5, size: 543 kB
Mar 4 score: 31.5, size: 543 kB
Mar 4 score: 32.9, size: 543 kB
Mar 4 score: 10.3, size: 719 kB
Mar 4 score: 10.3, size: 719 kB
Mar 4 score: 10.1, size: 719 kB
Mar 4 score: 10.0, size: 720 kB
Mar 4 score: 10.2, size: 719 kB
Mar 5 score: 16.0, size: 1132 kB
Mar 5 score: 24.2, size: 513 kB
Mar 5 score: 25.9, size: 513 kB
Mar 6 score: 9.9, size: 719 kB
Mar 7 score: 29.6, size: 699 kB
Mar 7 score: 12.3, size: 682 kB
Mar 7 score: 10.2, size: 433 kB
Mar 7 score: 10.2, size: 433 kB
Mar 7 score: 38.0, size: 543 kB
Mar 7 score: 38.0, size: 543 kB
Mar 7 score: 38.0, size: 543 kB
Mar 7 score: 7.5, size: 1787 kB
Mar 7 score: 18.1, size: 643 kB
Mar 7 score: 38.0, size: 543 kB
Mar 7 score: 38.0, size: 543 kB
Mar 8 score: 38.0, size: 543 kB
Mar 8 score: 18.2, size: 643 kB
Mar 8 score: 7.1, size: 1050 kB
Mar 8 score: 18.0, size: 1132 kB
Mar 8 score: 25.7, size: 501 kB
Mar 9 score: 30.6, size: 813 kB
Mar 9 score: 13.7, size: 779 kB
Mar 10 score: 36.9, size: 470 kB
Mar 10 score: 29.3, size: 1407 kB
Mar 10 score: 13.5, size: 910 kB
Mar 11 score: 8.0, size: 812 kB
Mar 11 score: 8.4, size: 821 kB
Mar 11 score: 25.5, size: 435 kB
Mar 12 score: 8.8, size: 857 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 12 score: 32.5, size: 543 kB
Mar 13 score: 32.5, size: 543 kB
Mar 13 score: 7.8, size: 732 kB
Mar 13 score: 7.9, size: 926 kB
Mar 13 score: 7.7, size: 732 kB
Mar 13 score: 19.9, size: 513 kB
Mar 14 score: 8.7, size: 821 kB
Mar 14 score: 8.8, size: 821 kB
Mar 14 score: 8.8, size: 821 kB
Mar 14 score: 8.7, size: 821 kB
Mar 14 score: 8.8, size: 821 kB
Mar 14 score: 8.7, size: 821 kB
Mar 14 score: 10.9, size: 564 kB
Mar 15 score: 22.6, size: 436 kB
Mar 15 score: 12.5, size: 558 kB
Mar 15 score: 8.3, size: 818 kB
Mar 15 score: 7.6, size: 818 kB
Mar 16 score: 28.5, size: 501 kB
Mar 16 score: 7.1, size: 925 kB
Mar 16 score: 11.3, size: 2484 kB
Mar 16 score: 9.1, size: 1964 kB
Mar 17 score: 7.0, size: 771 kB
Mar 17 score: 12.7, size: 539 kB
Mar 18 score: 23.8, size: 436 kB
Mar 19 score: 18.4, size: 499 kB
Mar 19 score: 30.3, size: 543 kB
Mar 19 score: 23.6, size: 435 kB
Mar 19 score: 23.0, size: 436 kB
Mar 19 score: 34.5, size: 543 kB
Mar 19 score: 34.6, size: 543 kB
Mar 19 score: 22.5, size: 513 kB
Mar 19 score: 23.9, size: 436 kB
Mar 19 score: 22.1, size: 512 kB
Mar 19 score: 22.5, size: 513 kB
Mar 19 score: 22.5, size: 513 kB
Mar 19 score: 34.6, size: 543 kB
Mar 19 score: 27.3, size: 513 kB
Mar 19 score: 7.2, size: 884 kB
Mar 19 score: 23.5, size: 436 kB
Mar 19 score: 28.1, size: 513 kB
Mar 19 score: 23.5, size: 436 kB
Mar 19 score: 28.1, size: 513 kB
Mar 19 score: 34.6, size: 543 kB
Mar 20 score: 34.7, size: 543 kB
Mar 20 score: 35.4, size: 543 kB
Mar 21 score: 10.8, size: 2925 kB
Mar 21 score: 37.0, size: 543 kB
Mar 21 score: 37.0, size: 543 kB
Mar 21 score: 20.6, size: 513 kB
Mar 22 score: 40.7, size: 470 kB
Mar 24 score: 29.1, size: 749 kB
Mar 25 score: 8.5, size: 625 kB
Mar 26 score: 22.8, size: 523 kB
Mar 26 score: 17.6, size: 1979 kB
Mar 27 score: 9.0, size: 577 kB
Mar 27 score: 14.8, size: 472 kB
Mar 28 score: 7.1, size: 542 kB
Mar 28 score: 9.4, size: 440 kB
Mar 29 score: 11.0, size: 578 kB
Mar 29 score: 11.0, size: 578 kB
Mar 29 score: 7.0, size: 7652 kB
Mar 29 score: 18.7, size: 691 kB
Mar 29 score: 28.8, size: 497 kB
Mar 29 score: 32.5, size: 497 kB
Mark
