[afnog] Spamassassin warning (was: Spamassassin help)

[Geert Jan de Groot]

Hi guys,

Just so you know, spamassassin has a nasty failure mode that
you should be aware of:
1. Spamassassin is reasonable CPU-intensive and hence makes a higher
   load on your mailserver
2. If the load peaks (for instance, because of a mail peak), the load
   may rise high enough so that the MTA temporary doesn't accept mail
   till the load drops a bit.
   It takes a while for the peak to get through the filter system,
   so the load stays a while
3. During this time, at various places in the world mail gets queued
   waiting for your MTA to accept mail again
4. Once the load lowers and the MTA accepts mail, the additional mail
   queued will raise the load again, which again causes the MTA to block.
   All the mailservers together trample the mailserver as soon as it
   accepts mail again, till it stops accepting mail.
5. Point 3-4 happen over and over, oscillating between accepting
   and not-accepting mail

The places where I've seen this, the ISP had no choice but to 
disable spamassassin for a while just to lower the floodgates.

To me, this effect came as a surprize the first time I saw it,
and I think you may want to be aware of it and at least monitor
the load on your boxes.

Hope this helps,

Geert Jan