We had an information store that had some corruption. We moved as many people off onto a new one as possible but were left with 4 we could not move. We tried a repair but it was taking too long so we canceled. This left the store unmountable.
Since it was just 4, we exported their email from the cached copy in Outlook, deleted the mailbox from the unmounted store, created a new one on the new store, and imported their email.
Everything is mostly working but intermiteantly they are getting non deliverable messages when someone from inside the company tried to send them an email. Email from outside seems to work all the time.
I tried several test from the Administrator account and was unable to get any failures but some internal people still get them.