[Mimedefang] Greylisting and Unknown User Question

[Mark Sheppard]

On 2004-06-22 (Tuesday) at 17:10:54 -0600, Lucas Albers wrote:
> Jeff Grossman said:
> > Is there a way to have Sendmail reject unknown users before I tempfail it
> > with greylisting?  Here is a log entry:
>
> I just tempfail all users, a few minutes later they get the permanent
> rejection notice anyway, so it should not effect valid users.
> I don't see any benefit to configuring it to not tempfail everything.

Whether or not it's desirable to delay greylisting until after the
valid recipient check depends on your greylisting implementation.
I've gone for a simplistic greylist that just checks whether the
sending IP has contacted us in the preceding 24 hours.  Using this
approach it's better to save greylisting until last so that if the
sending host sends to a valid address after trying several invalid
ones it gets greylisted.  If the greylist check was first then it
wouldn't.  To achieve this I just put the check at the end of
filter_recipient.

If you use the recipient address as well as the IP when determining
whether to greylist a message or not then the order of checks won't
affect the amount of messages that get through the filter.

Cheers,
Mark.