On Mon, Aug 09, 2021 at 08:29:29AM -0700, Ned Freed wrote:
In any case, the real question, I think, is not whether or not examples can be
found of incompatible use of this field - they can - but whether we want to
require implementation to support what is best a rare usage. Speaking for
myself, I think the answer should be "no".
The (at least dominant if not exclusive) present use of the field is
loop detection. In this case an MTA only needs to recognise the header
that it itself emits, and only for a matching addr-spec. All other
forms can be safely ignored.
The only other requirement is to not strip extant "Delivered-To" headers
when adding another. The order is not actually significant, but it is
best to prepend as with trace headers.
--
Viktor.
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