Mar 16 01:24:24 mail imap(someuser): open() failed with file /raid/mail/someuser/cur/1076979223.V416I136863.silverback.example .com:2,ST: Permission denied
I assume you've checked that "someuser" owns that file.
Yes.
Also check that every directory in the path is accessable to that user in the proper way. If it's NFS-mounted, the underlying mount point may have to have the correct permissions too (i.e., unmount the volume and have a look). An easy check is just to su to the "someuser" user and see if you can access the file in question.
It's a local raid and the permissions are (as far as I can tell) all correct as it works for long periods perfectly, then this error occurs. Sometimes restarting Dovecot fixes it, sometimes it doesn't.
Ah. Well, I was throwing in a couple of guesses to fill the silence - the error message does say that it's a problem with the mail file, not the index, though.
mm