Tom Hula asks,

> Which brings up a good question.  Why DO I sometimes (but not always)
> get a message saying the post was undeliverable ... looks like it was
> trying to process it as regular e-mail and couldn't ... but my post to
> the group (and I only post to the group ... don't use those combo
> features) works just fine.  Why is that?

There are any number of reasons why mail is "undeliverable" - either to a
friend, or to the list.

From a regular e-mail point of view, the reasons range from "unknown
mailbox" (the portion to the left of the "@" - which represents a mailbox or
an alias to a mailbox) is not known to the receiving server, to the fact
that the receiving server cannot speak to the sending server.

Basically, when you send a message, the SMTP server that serves you, takes
your message, and attempts to initiate a connection to the SMTP server
serving the remote domain (to whom you are sending).  There are a series of
commands which are executed back and forth, starting with HELO, for example.
When your local SMTP server tries to send various parts of the message, and
the remote SMTP server returns an error, your message is returned to you
(either immediately, or may be delayed) as undeliverable.  The error could
be any number of things though.

Another big problem is DNS (we have one right now, that we've been watching,
on the list, where a domain cannot be resolved, but we can't get rid of the
subscription)...  When a message cannot be sent, because your SMTP server
cannot resolve the address of the Remote SMTP server (an MX record in DNS,
which indicates the name of the server or servers), a DNS error occurs and
the message is returned.  It's like yelling "HELLO!  WHERE ARE YOU?" and
getting no answer back.

As for the list, if the message is sent to the proper address, then you
shouldn't have a problem.  Several things might cause errors though, and
they are the same things that plague regular e-mail (this IS regular e-mail,
after all).  For example, if someone works in an office, is subscribed to
the list, and then moves on, but does not unsubscribe - LISTSERV will
attempt to deliver the message.  Since that mailbox is no longer valid, you
get an "undeliverable" message (and sometimes, so does LISTSERV, which Jeff
or I need to deal with).  The reason YOU might get these is because LISTSERV
does not rewrite your headers, and as such, your REPLY-TO header is still
the same, and you get the bounce.

Hope this helps explain things a little.  I noticed that my "informal
survey" produced quite a few questions, which dovetailed right into this
question... such as "I don't know what my SMTP server software is - can you
tell me?".  Hopefully, this very simplistic explanation helps a bit.

(No, I wasn't going to get into the entire RFC on e-mail - that would make
this message, a novel instead).

Regards,
Joe