[Greylist-users] Better integration of greylisting module into exim4

[William Blunn]

> I'm using your greylisting module for exim since 6 month with great 
> success.
> 
> While porting exim4 to OpenBSD, I lobbied for including your work as 
> variant.

I must stop you there.

Martin's module, though functional and inspirational, has problems which
would make it a poor choice for inclusion into a package intended for
mass distribution:

Martin's module hooks in via local_scan(), which is much less good than
the alternative, hooking in via ACLs.

local_scan() is run at the end of message DATA, whereas ACLs are run at
several points during delivery.

local_scan() therefore suffers some disadvantages relative to hooking
via ACLs:

1. Some buggy MTAs ignore tempreject after DATA, resulting in messages
   being blackholed.  With ACLs you can tempreject at RCPT time, which
   is more likely to be correctly handled by a buggy MTA.

2. You still suffer the consumption of incoming bandwidth for rejected
   messages.  With ACLs you can tempreject at RCPT time, before the
   message DATA, thereby saving your incoming bandwidth.  (For delivery
   attempts with empty senders, it is advisable to defer tempreject
   until after DATA, in order to allow reverse address probing to work
   more quickly.)

Bill