If your Internet Mail Service (IMS) does not start, your inbound email will stop flowing.
If you have not run out of free space, a reboot may temporarily resolve the problem. You may notice that the Application Event Log may contain messages from the MSExchangeIMC service:
4070: An error occurred while opening a temporary message file. Verify that the message spool directories are configured correctly and are readable by the Internet Mail Service. 4131: An unexpected error occurred in the Internet Mail Service. Information about this error is stored in the data portion of this event.One possible reason for this problem is that the <Drive:>\Exchsrvr\Imcdata\In has been deleted. To fix the problem:
1. Create the <Drive:>\Exchsrvr\Imcdata\In folder.
2. Set Read permissions for Everyone on the folder, so users can't delete it.
3. Restart the IMS service.
If the folder continues to get deleted, enable auditing.