Aw: Re: [OT] CLI for noobies: The keys to GnuPG

[R. Hirschfeld]

> From: "Longman, Bill" <longman@sharplabs.com>
> Date: Fri, 2 Jul 2004 14:01:35 -0700 

> In addition, several other checks are used on some mail servers. The first
> is that the SMTP client needs to have a DNS entry for itself. Some even
> check to make sure that entry is an MX record.

Do you mean that the server does a reverse lookup on the IP address of
the incoming connection, and then a forward lookup on the result to
see whether there is an MX?  I've never encountered this in many years
of sending mail directly--I guess maybe I'm just lucky that none of my
correspondents' ISPs do this.  I never even had problems caused by the
PTR record not matching the domain I was using.  I did run into
anti-spam blocking when my ISP switched me from a static to a dynamic
IP address (which they just did and which has me considering switching
ISPs).  For now I've set my MTA to smarthost to my ISP's server.

> If you follow this idea, your MUA would have to connect to all the MX
> machines of all the people you email - a bit of a burden at the present
> time.

I suppose it could be a bit of burden if your machine is frequently
shut down or offline, as the queue of not-yet-delivered mail resides
on your own machine rather than on your ISP's server.  Otherwise it's
pretty straightforward.  It is your MTA rather than your MUA that
connects to the recipients' MX machines; your MUA just hands off to
your MTA, which handles the connections, queueing, etc. (I've heard
that some ISPs block outgoing port 25 connections except to their own
server, though, which would preclude connecting directly).

I fear this discussion may be drifting too far OT...

Ray