[ih] principles of the internet

[Tony Finch]

On Thu, 3 Jun 2010, John Day wrote:
>
> There is no MPL for mail.

If you mean "maximum packet lifetime" then how about RFC 5321 section 6.3:

   Simple counting of the number of "Received:" header fields in a
   message has proven to be an effective, although rarely optimal,
   method of detecting loops in mail systems.  SMTP servers using this
   technique SHOULD use a large rejection threshold, normally at least
   100 Received entries.  Whatever mechanisms are used, servers MUST
   contain provisions for detecting and stopping trivial loops.

Tony.
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