Matt,
In your implementation of Greylisting do you delay all mail for the
recommended 1 hour before allowing delivery?
there are several greylist implementations.
One used often with postfix is www.greylisting.org, called postgrey
and SQLgrey.
There is no fixed 1 hr delay. a triplet of ip/sender/recipient will
get past greylisting when it retires after the first 4xx greylist
rejection. automatic exceptions such as excepting a class C after
more than one IP get accepted, and excepting all senders from an IP
that retries.
greylisting is very effective against spambots on infected PCs
because they do not retry. I had one IMGate client who turned off
greylisting thinking it wasn't that effective. After immediate
clients complaints of increased spam, he turned it back on.
greylisting also greatly reduces the number of virus caught because
infected PCs are very often sending out infections.
Len
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