[Mimedefang] Poll: Other MTA's

David F. Skoll dfs at roaringpenguin.com
Tue Jun 11 15:24:05 EDT 2002

On Tue, 11 Jun 2002, Nels Lindquist wrote:

> I am, however, curious as to what kind of a framework you envision
> for this.  I'm assuming there would have to be MTA-specific
> functions, depending on whether the MTA supported milter-like
> capabilities or not?

What I envision is a daemon which listens on port 25 and relays commands
to the real mail server.  So you have something like this:

+-----------+         +---------+             +-----------+
|  Sending  |-------->|	MDefang |------------>| Real SMTP |
|   Relay   |<--------|	Daemon 	|<------------|	Server 	  |
+-----------+         +---------+             +-----------+

The MDefang Daemon and the Real SMTP Server may or may not reside on the
same host.  Scenario:

Sender -> MDefang                  EHLO
          MDefang -> Real Server   EHLO
          MDefang <- Real Server   220 foo.bar.com ESMTP
Sender <- MDefang                  220 foo.bar.com ESMTP

... etc

So the daemon "listens in" on the SMTP conversation.  (It can do
processing before deciding to forward a command from the sender to the
real server.)  If the message is rejected, for example, it sends a
RSET instead of forwarding all the message content.  Some abilities
will be lost -- there's no way to delete recipients based on message
content, for example, and any sort of IP-based blacklisting or relay
control will have to be done by the MDefang Daemon.

It might be a convenient and simple way to get MIMEDefang to work
with any mail server, though, so the tradeoffs might be worth it.
Be assured that even if I implement this, the Milter version will
still be the main one and the one with best features and support.



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