Path: utzoo!utgpu!news-server.csri.toronto.edu!neat.cs.toronto.edu!rayan
Newsgroups: comp.mail.sendmail
From: rayan@cs.toronto.edu (Rayan Zachariassen)
Subject: Re: A general question of mailers
Message-ID: <90May26.200545edt.22250@neat.cs.toronto.edu>
References: <9300002@ux1.cso.uiuc.edu>
Date: 27 May 90 00:06:30 GMT
Lines: 39

Phil asks why bother validating the Mail From: address synchronously.

The answer depends on religion and economics:

Synchronous address validation gains you:

	- economy of data transfer, i.e. you only move the message
	  over the link if the receiving mailer isn't going to immediately
	  return it due to a problem in the SMTP envelope.

	  This is a matter of $$s to people who pay volume charges for
	  their IP links (e.g. IP/X.25).

	- real-time feedback from the SMTP server about the acceptability
	  of the mail.

	  This is the religion part... some people insist on having this
	  warm fuzzy feeling.

... but costs you:

	- latency, which relates to general robustness (the longer the
	  SMTP connection is established the higher the chance of something
	  going wrong), and affects the queue sizes on the SMTP client
	  machine.

	  On busy mail relays/gateways, this can be a significant effect.

	  If you pay time charges for your mail link (e.g., IP/X.25 on
	  some PDNs), this can also be a $$ concern.


On fixed-cost high-bandwidth links, I'm a firm believer in Asynchronous
address validation.  I call it the HOT ROCK model of message transfer
(let somebody else closer to the destination worry about the message,
ASAP).  It certainly keeps the queues down on busy mail machines.
I think that's pretty important to the quality of life on those machines.

rayan