A guess would be that this is likely due to the endianess of the multiple architectures that the index is being accessed with. We have the same issue here across i686/x86_64/sparc. I'm about to post to an older email thread about this as well.
Michael D. Godfrey wrote:
System: Linux 2.6.25.6-55.fc9.x86_64 #1 SMP Tue Jun 10 16:05:21 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux Dovecot: dovecot-1.0.14-8.fc9.x86_64
We have used Dovecot for several years. The error message below appears in the system log quite frequently. I have run a test which shows that this message is due to 2 or more users accessing the same mail (i.e connecting using the same userid). This happens for various reasons including the fact that some users have their client machine set up (typically using Thunderbird) with more than one account within a single Thunderbird configuration. Thus, more than one person may be reading or sending mail from a single Dovecot account.
The Dovecot error is:
Dovecot disconnects: Inactivity: 13 Time(s) Logged out: 2 Time(s) in IDLE: 12 Time(s)
**Unmatched Entries** dovecot: IMAP(godfrey): Connection closed: 4 Time(s) dovecot: IMAP(godfrey): Corrupted index cache file /home/godfrey/Maildir/dovecot.index.cache: invalid record size: 1 Time(s) dovecot: IMAP(igodfrey): Connection closed: 4 Time(s)
or: Dovecot disconnects: Inactivity: 23 Time(s) Logged out: 1 Time(s) in IDLE: 6 Time(s)
**Unmatched Entries** dovecot: IMAP(godfrey): Connection closed: 8 Time(s) dovecot: IMAP(godfrey): Corrupted index cache file /home/godfrey/Maildir/.Sent/dovecot.index.cache: invalid record size: 1 Time(s) dovecot: IMAP(godfrey): Corrupted index cache file /home/godfrey/Maildir/dovecot.index.cache: invalid record size: 1 Time(s) dovecot: IMAP(igodfrey): Connection closed: 6 Time(s)
---------------------- Dovecot End -------------------------
These errors do not seem to cause any serious problem, but it would be good if the problem could be fixed.
I have seen other "corrupted" error reports in the mail archive, but they did not seem to be exactly like this one.