|Okay, I think you're on to something here- I've seen the same type of
|question about my list ([log in to unmask]) regarding multiple
|processing hosts. Unfortunately, what you wrote above goes *right* over my
|head. Can I play clueless newbie and ask for a little more explanation?

The MOST important aspect is to understand that when someone (thing)
specifically uses the Internet to send SMTP (email), as opposed to HTTP,
FTP, NNTP (NETNEWS), TELNET, etc., that the resolution (lookup) of the
hostname to IP address is different from those other xTP processes.

Basically the SMTP client process first asks the Domain Name System if the
hostname has any "MX" Resource Records available.  If so, it recurses the
lookup of those hostnames looking for an "A" (IP address) R.R.s.   It then
prefers to try to send to those hosts in precedence (arithmetically low to
high order) where the lower numeric values are considered to be of higher
precedence.  The first such host to respond successfully to the SMTP dialog
is the "winner" of the resultant transfer of data.

What that host does with the mail is a matter of local configuration.
E.g., it might forward it to a userid lookup scheme such as CSSO/PH, or
send it directly to the userid mailbox.  It might sit on some q for a long
time.  It might bounce.  it might do nothing.  Just like any mail.

When you deal with multiple such hosts, it is clear that depending upon
which one actually received the mail might lead to different results then
when one of the other ones does.  (Different hosts for different strokes? ;-))


Date:         Mon, 19 Jun 1995 16:09:00 EDT
From:         "Peter M. Weiss +1 814 863 1843" <[log in to unmask]>
Subject:      Overview: Electronic Mail Delivery

(Permission granted to reprint, though you might want
to edit for your specific installation.  PMW1)

Determining failure locations in electronic mail requires
an understanding of numerous network functions and layers.
Often times, that is the work of an e-mail postmaster.
Most e-mail sites support a generic e-mail address of
[log in to unmask]  The job of postmaster is often done
as an 'other duty as assigned' or in rare instances,
not at all.

As you will see, e-mail just doesn't "happen" but is the
result of a complex interaction of computer processes.

In general, the ability to successfully transmit electronic
mail (e-mail) from a LAN-based system is due to the proper
administrating and functioning of:

1) the client software -- typically a package like Eudora
installed on a workstation

2) your office/department LAN as operated by your system
administrator

3) a mail gateway/server such as that operated by the
Center for Academic Computing

4) a data backbone such as that operated by the Office
of Telecommunications, and those of external service
providors

5) the Domain Name System such as operated by a number of
inter-dependent host sites including the Office of
Telecommunications, many times in conjunction with other
departments and/or external institutions or individuals

6) the proper operation of telecommunication circuits
usually operated by local exchange and long distance
carriers

7) the proper administration of any name (userid) lookup
schemes which is controlled by both system administrators
and mail users such as operated on PSU.EDU (PH) facilities

8) the proper operation of the receiving mail server
such as that operated by the Office of Administrative
Systems aka oas.psu.edu

9) the proper administration of the receiver's mail
box, as impacted by various security software, as
well as the receiver him/herself (not allowing the
mail-box to overflow)


(When e-mail is sent to a LISTSERV-based list, the
delivery mechanisms are even more complex.  Fortunately,
there are personnel at Penn State who can help trace
that flow.)

/Pete Weiss,
[log in to unmask]

--  co-owner INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
[log in to unmask]        "I get paid by the Byte"        +1 814 863 1843
31 Shields Bldg. --   Penn State    -- University Park, PA 16802-1202 USA






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