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Subj:	Re: VMS "NMAIL"

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Date: 9 Sep 89 12:09:49 GMT
From: shlump.nac.dec.com!cheese.enet.dec.com!kaiser@decuac.dec.com
Organization: DEC Systems Consulting Group
Subject: Re: VMS "NMAIL"
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In article <4105@tansei.cc.u-tokyo.JUNET>, c31293@tansei.cc.u-tokyo.JUNET (Kenji Rikitake) writes...
>What is VMS "NMAIL"? Obviously, it's not bundled with a standard
>VMS distribution kit (without DECnet). What kind on the software
>it is? Is it a DEC product? Or a DECUS software? Or else?

Nmail is a package, available through the ASSETS library (more below), at least
in the United States, to improve ease-of-use of VMS MAIL.  I'll explain, but
first some background.  Forgive me if you already know all this.

There are two philosophies of doing network mail.  One is the store-and-forward
method typified by Internet mail: a completed mail message is passed from host
to host on the network, stored in its entirety on each host until the next is
capable of taking it, until it eventually reaches its final destination and
user.  The other, typified by VMS MAIL, is that a message won't be sent at all
unless a connection to the final destination (machine and user) can be estab-
lished and maintained at the time of transmission.

ADVANTAGES of store-and-forward: you never have to wait for a connection to be
established and maintained all the way to the target, but when your message is
ready to go, it just starts on its way without delay, making its way from host
to host until it reaches its target.  DISADVANTAGE: things can (and sometimes
do) go wrong on the way, and mail gets bounced back to you.  For instance, one
of the machines on the path, which you've never heard of, times out while
waiting for the next machine to take your mail, and sends your message back to
you with a "bounced" message.  Or your message reaches its target host but the
target user doesn't exist (perhaps you misspelled the name), or one of the
machines on the path has screwed-up mail configuration files.  Anyhow, you
thought everything was okay, but three days later you get back your original
message with an explanation of why it didn't arrive.

ADVANTAGES of (what's the right name for this?) complete-connection mail: when
your mail is complete, you KNOW that you have a good path to the target and the
target user, so you're effectively guaranteed that your mail arrives properly.
DISADVANTAGES: first, that you can't always send your message NOW, because you
may not be able to get a complete path at the time you want to send; and second,
that you have to sit and wait while the entire message (perhaps a long one) is
transmitted to its target.

Which you prefer is a matter of taste.  Nmail attempts to combine the advantages
of both in what its author has called "stash-and-heave" mailing.  Here's how
Nmail works.  You use VMS MAIL as usual, with Nmail as the transport (either by
specifying Nmail as the transport, or by using the foreign mail "NM%" prefix on
the target address).  Your message is immediately put on a queue managed by
Nmail, which attempts to make a non-Nmail mail connection with the target.  If
the connection can be made, off goes the mail.  If either the host isn't known
or the user doesn't exist, you get notification back quickly.  If the host is
known but inaccessible, your message is kept queued and is retried on a
(configurable) regular schedule for a (configurable) fixed period, and only if
that period runs out is your mail returned by Nmail to say it couldn't be sent.

Nmail is used extensively within Digital, since on a network the size and extent
of ours, it's a certainty that some machines will be down at any given time for
backup, maintenance, repair, or other reasons.  Nmail gives us the convenience
of store-and-forward with the reliability of guaranteed connections.  (Oh my
lord, I sound like a salesperson!)

It's been made available, at least in the U.S.A., through ASSETS.  ASSETS is a
library of software, most developed internally for our own use or as midnight
hacks, that's so useful someone wanted to buy it, but which, for one reason or
another, we don't want to turn into a full product.  ASSETS packages are sold, I
think, as installation-plus-binaries.  Salespeople can provide literature.

---Pete

kaiser@cheese.enet.dec.com
DEC, 2 Mt. Royal Ave. (UPO1-3), Marlboro MA 01752-9108
508-480-4345 (machine: 617-641-3450)