Hallo Stephan,
Hmm. Probably, the timezone configuration (i.e. the contents of TZ timezone environment variable) somehow doesn't reach the final stages of e-mail delivery.
I investigated further.
I just did a telnet into the server and discoverered that dovecot knows the localtime. If I ask for the INTERNALDATE of a message the 2 hour offset of CEST is actually in the response:
a fetch 166 INTERNALDATE
- 166 FETCH (INTERNALDATE "02-Aug-2015 20:18:21 +0200") a OK Fetch completed (0.000 secs).
See? The message above actually arrived at the server at 22:18 localtime. The Date-Header is set accordingly.
The file modtime is being set to 20:18 of that day (for whatever reason). So the server responds with that time and adds the correct TZ offset (2 hours). So my assumption is that dovecot knows that we are at CEST (+0200).
It's a maildir storage and the mails are received by netqmail-1.06. The last dovecot which we were using was version 2.2.14.
With this version and system init and Mandriva 2010.2 we didn't have this kind of problem. I'd really like to understand this because some apple clients are having huge problems with the hours old INTERNALDATE.
Thank you for your time.
Greetings
-- Christoph Gröver