Milter-greylist

Russell Bell wrote:
 > I turned on milter-greylist for everyone in my domains after it
 > worked well for me and the volunteers.  Unfortunately some messages
 > have been delayed for many hours, one as long as 93.  I used the
 > default; the log tells me they were all delayed for 30m.  Could it be
 > anything other than the sender giving up before 30m has expired and
 > not coming back for hours?

That can happen if the message is being sent from an ISP
with a large number of outgoing mail servers with different
IP addresses, and they try to resend the mail from random
addresses.

That means that the second attempt comes from a different
address than the first one, so milter-greylist creates a
new tuple, and the greylist interval starts over again.
If the third attempt comes from yet another address, the
same happens again, and so on, until the delivery attempt
happens to come from an IP address that milter-greylist
has seen before.

You can alleviate the problem in many cases by using the
"subnetmatch /24" option in your configuration, so milter-
greylist will ignore the lower 8 bits of the IP address,
assuming that the whole net belongs to the same ISP.  That
assumption isn't always true, but the setting seems to work
very well in practice.

If your users receive many mails from that particular ISP,
you could alos try to enable the "lazyaw" option.  It will
add IP addresses of successful deliveries to the whitelist,
no matter who sender and recipient are (by default, the IP
is only whitelisted for that particular sender+recipient).

Best regards
   Oliver

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