[TriLUG] Fwd: mail relay through trilug.org?

[Tanner Lovelace]

On 7/10/07, Scott Lambdin <lopaki at gmail.com> wrote:
> On 7/10/07, Tanner Lovelace <clubjuggler at gmail.com> wrote:
> >
> > Port 587 - (See RFC2476).  This is the mail submission port.  It only
> > takes
> > incoming mail from mail clients, not mail servers. (I believe)  You must
> > first do STARTTLS to encrypt the channel, then SMTP AUTH to log in
> > and only then will it let you relay mail.
>
>
>
> I think clients and servers are not distinguishable in smtp.
>
>

No, you're not looking at it correctly.  Postfix on ports 25 and 465 are acting
as "Mail Transfer Agents" or MTAs.  On port 587 it is acting as a "Mail
Submission Agent" or MSA.  From the RFC 2476:

   SMTP was defined as a message *transfer* protocol, that is, a means
   to route (if needed) and deliver finished (complete) messages.
   Message Transfer Agents (MTAs) are not supposed to alter the message
   text, except to add 'Received', 'Return-Path', and other header
   fields as required by [SMTP-MTA].

   However, SMTP is now also widely used as a message *submission*
   protocol, that is, a means for message user agents (MUAs) to
   introduce new messages into the MTA routing network.  The process
   which accepts message submissions from MUAs is termed a Message
   Submission Agent (MSA).

So, yes, in this case, they are definitely distinguishable.

But, even in the general case, mail clients like thunderbird speak SMTP.
No one will argue that T-bird is a server, so I fail to see what you're getting
at here.  SMTP is a client server protocol, which means that there will
be clients and there will be servers.  Servers may then turn around and act
as clients too, but they don't have to.

Cheers,
Taanner
-- 
Tanner Lovelace
clubjuggler at gmail dot com
http://wtl.wayfarer.org/
(fieldless) In fess two roundels in pale, a billet fesswise and an
increscent, all sable.