Timo,
With a few tests I didn't notice any problems though.. Does that happen with all emails? Does it matter if you delete dovecot.index.cache file for the mailbox? Could you look at the ENVELOPE reply if it contains the sender? (http://dovecot.org/bugreport.html#sniffing)
It does happen with all emails and it happens with the cache file deleted (as matter of fact, I deleted the entire maildir directory and created a fresh one, delivered mail to it and started OE).
I used Ethereal to sniff the connection to Dovecot. The EVELOPE command is:
ENVELOPE ("Fri, 4 Mar 2005 10:16:24 +0100" "Test" NIL NIL NIL NIL NIL NIL NIL "<001001c5209a$d67d5e80$f7572582@lap04XXXXX>") RFC822.SIZE 1377 UID 11 FLAGS (\Recent) INTERNALDATE "04-Mar-2005 10:16:02 +0100") i36i OK Fetch completed.
You can see the entire output on: http://www.luckyhands.nl/download/dovecot-envelope.txt
Best regards, Remy