Mail stops flowing in exchange 2007 or exchange 2010, in event viewer you see the event id 15006 and The Microsoft Exchange Transport service is rejecting message submissions because the available disk space has dropped below the configured threshold. This can be fixed by moving the mail.que file.
On a fresh Exhange 2013 install you cannot log into the ECP/EAC and receive the error Server Error in ‘/owa’ Application. The Active Directory user wasn’t found.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.