On Fri, Aug 13, 2021 at 11:02:19AM -0700, Dave Crocker wrote:
On 8/12/2021 7:49 PM, John Levine wrote:
As far as we know, all of the existing usage is for loop detection, so it
would
be reasonable to say the contents of the header is a token or sequence of
tokens
The strings we have documentation for do not look nearly as abstract
as the term token implies. Rather, they look like email addresses.
The above shows a profound unwillingness to look beyond the apparent
syntax to the semantics committed to by the MTAs that are using this
header. The extant implementations of "Delivered-To" make no promise
to record anything recognisable to any party other than the MTA.
At least in the case of Postfix, we specifically go to the trouble of
optionally prepending a separate "X-Original-To" header which records
the input address that led to the recipient, which in contrast to
"Delivered-To" is specifically intended for consumption by downstream
user agents.
It is not acceptable to violate the interface *contract* and saddle the
"Delivered-To" header with new semantics, whereby the recorded address
is anything other than an opaque token. If that's the inention, you can
end the experiment now. No such commitment will be made in Postfix, the
header payload will remain a private nonce for exclusive use by the MTA.
No matter how many times you repeat that "Delivered-To" is in practice
observed to be some variant of an actual email address, Postfix will
retain the right to use some other semantics that, while conforming to
an "addr-spec", may hold something that only the generating MTA can
generate and recognise.
--
Viktor.
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