[Dovecot] Error: unlink_directory(.../lucene-indexes) with doveadm index

Hi,

Per discussion on this previous thread: http://dovecot.org/pipermail/dovecot/2012-October/068849.html

I am updating search indexes on all my mailboxes via a nightly cronjob that runs: doveadm index -A '*'

The problem we're running into is that random mailboxes will throw the following error during the update (sanitized to conceal actual domain name):

doveadm(user@domain.com): Error: unlink_directory(/var/spool/mail/domain.com/user/sdbox/lucene-indexes) failed: Permission denied

We have around 250 domains on the server, with a handful of mailboxes on average in each domain. We get this for a varying number of total mailboxes (1 to 6 every night). It is common for the same mailbox to show up a few days in a row and then stop throwing the error. The script is running as root, so there shouldn't be any file level permissions.

Any thoughts on the root cause of these errors? What can I provide to help further diagnose?

Thanks, Fred Kilbourn