[Greylist-users] recommendations for dual MX system?

Graham Toal gtoal at gtoal.com
Mon May 2 09:11:52 PDT 2005

> The overhead of administering mysql is unbelievably trivial, but never mind.
> There's never time to do it right, but there's always time to do it again.

Sometimes that's not such a bad thing :-)  A paper that was very influential
on me in my youth was:


I will have time to do it again right in the long term, but just take
my word that right now it is politically expedient to come up with
something that works well and won't mess up the email of tens of
thousands on people, on a time scale of a few days or a week at
most, but not months.  In the short term that means some clever
hack with spamd, whether sharing the routing tables, or the greylist
db entries.

Mark Pecaut suggested, in an off-list mail, a rather clever but
complex hack:  if you have two MX hosts to do greylisting but
give them different MX priorities, most of the traffoc should
go to the lower-numbered one.  Assuming one server has no problems
routing all the campus email through it, then you get the load
balancing by having pf distribute the connections *after* they
are whitelisted on a round-robin basis to the two back-end
mail servers 9which do the heavyweight spam filtering and virus
checks that we still need).

You get the redundancy of keeping the dual paths because if the
primary MX fails, it backs off the the other MX greylist box -
which admittedly has to build up its tables again - and it too
does the same pf trick to distribute the mail across the back-end

I'm tempted by that one except that the complexity of the routing
rules may be more than I'm up for at this early stage in re-learning
bsd after a long absence.  It is however my backup plan unless
someone has a better one! :-)

What would be perfect would be if when spamd creates a GREY
entry in its database (or promotes a GREY to WHITE), it also
notifies all other spamds in the same cluster that they should
do the same.  However that's a feature enhancement for the
future.  Right now I'm hoping there's some easy hack to get the
same effect externally.


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