My client is using hosted exchange from Rackspace and they are still on the old Exchange 2007 platform there. They have upgraded to Office 2013 and now they are consistently, annoyingly prompted for password for that email account. What we have done that has not worked to remove the prompting:
1. deleted and recreated OST
2. deleted stored credentials
3. requested the client have the mailbox moved to a newer exchange at Rackspace, (no good as they have no control over this)
They and I are at wits end. Hopefully someone has an answer that does not involve server side changes as we have no access to that at all.