Milter-greylist

Da Beave wrote:

> 
> 	I friend of mine brought up a interesting idea.   Basically, 
> "autowhitelisting" via Subject: .   Basically,  if the subject contains
> a "certain string" in the Subject: line,   it'll automatically be 
> autowhitelisted.   This way,  for those 10% of people in our case,  they
> would request that when people e-mail them to put a special "secret" 
> string in the Subject: which would "autowhitelist" the inbound mail.
> 
> 	Something like a "acl whitelist subject",  then you could 
> put in the regexp you wish (your secret, for example).

Problem.. at the point the greylist-or-not decision is made, there is no subject
yet. In fact, there aren't any headers at all, only the connection and the
envelope information.

You only get the subject line (and any other message headers) as a part of the
DATA phase, and you have to wait for it ALL to be transfered.

At that point, greylisting the message could be really detrimental to your
network utilization, especially if the message is large and/or the sender has a
fast retry rate on 4xx errors.

The only things available are:
 1) the connecting IP
 2) the RDNS lookup of that IP (if any)
 3) the HELO string (if any)
 4) the MAIL FROM: (envelope sender)
 5) the RCPT TO: (envelope recipient(s)).