Microsoft: October Windows Server updates break Exchange sign-in, mail flow

Microsoft has confirmed that this month's Windows Server security updates are causing OWA sign-in and mail delivery issues on some Exchange Server systems. In some cases, affected customers are also reportedly seeing Exchange Server OWA failing with a "MapiExceptionMdbOffline: Unable to make connection to the server. (hr=0x80004005, ec=1142)" error and Event ID 1006 in the application log.