Since this thread is of great interest to me, I want to pipe up here to
ensure that not too much weight is put on the Received-header.
Harald Reindl suggested to grab the recipient from the Received:
headers instead (rather than from "Delivered-To": or "Envelope-to:"),
and I second that.
The Received-header does not necessarily contain the e-mail address that
the message was delivered to. And even when it does, it may contain
someone else's address entirely. Since the primary purpose of the
"Received:"-header is to track the messages route as it passes from one
mail server to the next, the recording of the destination e-mail address
has been severely restricted. See:
http://tools.ietf.org/html/rfc5321#section-4.4
Specifcally, only one recipient address may be mentioned in a
Received-header. And that is entirely optional.
Assuming the recipient's mail server is used by more than one party on a
mailing list, and the previous mail relay submits the message in a
single transaction, and the recipient's mail server includes the
so-called "for clause", the e-mail address of exactly one of those
parties will be in the "Received:"-header, and that just might be an
address that is different from the recipient currently looking at it.
Often, though, the for clause is just left out.
Matching identities is a creative endeavor by design. And taking
advantage of fields offered by MTAs that are dedicated to informing mail
clients about what the final delivery address was seems a more reliable
way to go (i.e.: Envelope-To and Delivered-To). Currently, there is no
RFC that prescribes a field that can be reliably used for the purpose of
matching identities to the final delivery address of an e-mail.
Personally, I would suggest looking at all fields known to be of value
for this purpose, ordered by reliability (including Envelope-To,
Delivered-To, and Received, in that order).
Cheers,
Sebastian
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*Sebastian J. Bronner*
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