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Sometimes this issue is caused by a misconfiguration or incompatibility of the Exchange server, or perhaps by a bug in Mail. If so, you won't be able to resolve it yourself. The fact that your iOS devices may be working well with the same account isn't relevant, because iOS uses a completely different protocol (ActiveSync) to communicate with Exchange servers. By default, OS X Mail uses the EWS protocol.
Each of the following steps has been reported to help with Exchange issues, at least temporarily, in some cases:
1. Back up all data. Open the Internet Accounts pane in System Preferences and check to make sure you don't have duplicate Exchange accounts. If you do, delete all but one of the duplicates. If there are no duplicates, delete the account and recreate it with the same settings.
2. Rebuild the affected mailbox.
3. Reindex messages.
4. Follow the instructions in this support article to disable autodiscovery. You may need to get configuration details from the server administrator.
5. In the Keychain Access application, delete the password item for the account. The next time Mail tries to access the account, you'll be prompted for the password. Check the box to save it in the Keychain.
6. If you've created subfolders of the Exchange inbox, log in to the server through its web interface, move the messages out, and remove the subfolders. The inbox should have no subfolders.
7. Synchronize with the server using IMAP rather than EWS. This is only possible if IMAP is enabled on the server.
8. Consider using Outlook instead of Mail to access your Exchange mail.
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See also this discussion.
Office 365 Os X Yosemite Dmg
Nov 22, 2014 9:49 PM