Some emails about changed talk pages arrive twice, with different message ids. (Also, they are apparently held up for hours at wiki-mail.wikimedia.org.) An example (from hu.wikipedia, User:Bitman):
Date: Sat, 28 Feb 2009 18:06:47 +0000
Message-Id: <E1LdTaJ-0005r9-Dg@mchenry.wikimedia.org>
Date: Sat, 28 Feb 2009 18:06:46 +0000
Message-Id: <E1LdTaI-0005pq-4C@mchenry.wikimedia.org>
Version: unspecified
Severity: minor