Another related issue is whether "Message-ID" should be the
same or different, when a message is sent to some
recipients with "Bcc" headers and to other recipients
without.
Arguments for the same Message-ID: This means that threads
will be intact for all recipients whose mailers use the
Message-ID to keep track of threads.
Arguments agains the same Message-ID: Many mailers suppress
multiple copies of the same message with the same
Message-ID. Thus, if a person receives two copies of a
message, one with and one without Bcc, then depending on
the order of reciept, only one of them will be retained.
Of course, the ideal mailer, which suppresses multiple
copies of a message, should merge the headers of the
multiple copies, but this is not very commonly done.
--
Jacob Palme <jpalme(_at_)dsv(_dot_)su(_dot_)se> (Stockholm University and KTH)
for more info see URL: http://www.dsv.su.se/jpalme/