Subject: smtpupd-09 still requires ``stopping trivial loops''

From: "D. J. Bernstein" <[email-masked]>
Date: 30 Jan 1999 18:40:23 -0000

> Whatever mechanisms are used, servers MUST contain provisions for
> detecting and stopping trivial loops.

This requirement is horrendously vague.

Is it enough for a server to reject messages that don't fit onto disk?
This does detect and stop most loops---eventually.

The document editor ignored my previous request for definitions. That's
not acceptable. Protocol specifications must be clear.

---Dan

---

From: [email-masked]
Date: Sat, 30 Jan 1999 21:33:39 +0200 (GMT)

> This does detect and stop most loops---eventually.

   I suppose Dan is trying to be sarcastic.
In real world we see systems counting "Received:" headers, and when
the number of those exceeds some threshold value, a loop is reported
and possibly stopped.  That is the most low-tech approach around, but
quite efficient.

> not acceptable. Protocol specifications must be clear.

  The document editor is asking *everybody* for a definition text,
why don't you supply something ?

I will try:

  One method to detect loops is to count the number of "Received:"
  headers in the incoming message.   When the count  exceeds set
  threshold value, the message can be considered looping.
  Suggested minimum value for the threshold is: 20

  Most often a person-to-person  inter-system  communication can
  happen with two or three processing steps, however email lists
  may need in order of 10 steps to go thru.  Corporate firewalls
  may add one, or two steps more.  A message redirection at some
  location from one address to other adds usually one or two more
  steps.

There are other schemes around too, I believe Dan has created one
of them.

> ---Dan

/Matti Aarnio <[email-masked]>