On 8/9/2021 1:41 PM, Rolf E. Sonneveld wrote:
The key unanswered question is what the "audience" for the header
content
+1
A nice example of the proverbial solution in search of a problem.
From the Introduction, what about this is insufficiently clear or complete?
Given aliasing, mailing lists, and the like, the transit of a message
from its author to a final recipient might include a series of
submission/delivery events. Also, the delivery process can produce
local address transformations. It can be helpful for a message to
have a common way of indicating each delivery in the handling
sequence, and to include each address that led to the final delivery.
This can aid in the analysis of a message's transit handling. An
additional use can be for detecting a delivery sequence loop. With a
loop, the same copy of a messages transits the same email address
more than once. This is different from having the message simply
transit the same MTA more than once, which might be necessary, such
as when it is processed through a mailing list; an MTA services many
addresses. It is also different from having two copies of the same
message arrive at the same, ultimate mailbox, having been originally
posted to two different addresses.
Delivering the same copy of a message more than once, to the same
address, is almost certainly not an intended activity. An example of
a problematic arrangement would be to send a message to mailing list
listA, where listA contains an entry for listB, and listB contains an
entry for listA. The message will enter an infinite loop. Loop
detection for email can be a complicated affair. The Delivered-To
header field provides helpful information with a definitive
indication that this copy of a message has been delivered to a
specific mailbox.
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
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