If a customer reports that some of their mail messages are suddenly disappearing and you can't discover the cause, you can try regenerating the mailbox index file. Although rare, if a corrupted index file caused the problem, reindexing will fix the problem.
Note: This feature is only available to company and company mail administrator levels.
Before reindexing the mailbox, you should check to see if the messages can be restored using the restore email tool. If the messages are not available to be restored, then you can try reindexing. Reindexing a mailbox will terminate any existing POP3 and IMAP4 connections, and cause the mailbox to be unavailable for a few minutes. You should only do this if you have ruled out all other causes as reindexing will log off the user if they were logged in, and their mailbox will be unavailable for several minutes.