A few minutes ago I checked my Outlook 2013 client (connected to an Office 365 email server) and it reported no new emails. I knew there was at least one pending (my smartphone had already reported it) so I tried clicking on the Send/receive button. It seemed to hang, but finally after many minutes it popped up this dialog box:
Note the "CONNECTED TO: MICROSFT EXCHANGE" on the status bar and yet the dialog box reports it can't connect to the server to get the pending email. It is now many minutes later and the email has still not arrived, also the status bar has changed to "TRYING TO CONNECT".