[Greylist-users] Exim 4 ACL - greylisting only outside hosts

[William Blunn]

> I think you're misunderstanding the intent of having the filter see
> outbound mail.

In fact I didn't know what it was for at all :-)

> It isn't so it can delay the mail,

which would be a bit pointless :-)

> it's so it can add records to the db so that replies to the outbound
> mails won't be delayed.

I can see the logic in that.

> See the reverse_track code in my milter.

I will see about fitting that into the next chunk of available time.

I am guessing we can query for, and if not already present, store a
record for, something like this:

   host:      match any
   sender:    the recipient of the outgoing message
   recipient: the sender of the outgoing message

i.e. swap the sender and recipient before doing a database query or
storing new records.  This way the record(s) should be found by the
normal database query without requiring a separate query.

If the recipient does send a reply, then when their reply comes
through, we will match on this record, and if we don't have a host
address, we can store that in the database.

We will want to expire those records at some point.  Although the
records have a wild host match, it's probably very unlikely that a
spammer will chance across that exact sender-recipient double.  So it
would be safe to leave those records in there for a month I guess.

The greylister will need to know whether messages are incoming or
outgoing.

For my freestanding binary implementation I could put in an optional
command-line switch to identify outgoing messages, and then make Exim
invoke it accordingly.

Bill