[AusNOG] Greylisting in an ISP / Hosting Environment

[Tim Warnock]

>While it does reduce spam, you run into the problem where some ISPs and
>corporates attempt delivery from different outbound IP addresses with each
>retry period. If you are greylisting on a combination of sender IP,
envelope
>sender and envelope recipient (or even just the first two) then it's
>possible that incoming mail will be significantly delayed.

Some greylist daemons allow you to specify a subnet size to search, so if
you are being hit by several IP addresses within say a /23 it will consider
it to be from a single source.