Zitat von Martijn Brinkers <martijn(a)djigzo.com>om>:
Exchange duplicate detection:
Duplicate detection of delivered messages is done by the Exchange store.
The store does duplicate detection based on two properties on the
message - the Internet Message Id and the client submit time. We would
have liked to do duplicate detection based solely on the Internet
Message Id but there are several not-to-be named applications out there
that use the same Internet Message Id on all their messages.
This is broken by design. The message-ID is a MUA thing and therefore
should never be changed by any MTA. If Exchange does not use the
recipient mailbox *and* the message-ID to supress duplicates the
developer have probably not read any RFC. But maybe they have learned
From RFC 2822 section 3.4.6
In all cases, it is the meaning that the sender of the message wishes
to convey (i.e., whether this is the same message or a different
message) that determines whether or not the "Message-ID:" field
changes, not any particular syntactic difference that appears (or does
not appear) in the message.