Jacob Palme <jpalme(_at_)dsv(_dot_)su(_dot_)se> writes:
Keeping a data base of Message-Ids to recognize duplicates is rather
easy, if you do it the way I once did it. I kept the data base to a
fixed rather low limit. This means that my software would not recognize
duplicates if they arrived at widely different times, but this does not
happen in reality. The fact that all duplicates typically arrive the
same day or at least the same week makes the implementation of such a
data base much easier.
Detecting duplicates is relatively straightforward; my mail client does
that out of the box. The hard part is then choosing *which* duplicate to
suppress, while still not showing the mail message to the user twice or in
the wrong location in their mailbox sorting.
--
Russ Allbery (rra(_at_)stanford(_dot_)edu)
<http://www.eyrie.org/~eagle/>