If Outlook 2013 on Rackspace stops receiving email follow these steps to resolve the problem.
Click on the FILE tab
This screen appears, press ‘Account Settings / Account Settings
This windows appears, highlight email@example.com and press the Change button.
This window appears, press the ‘More Settings’ button.
This window appears, click on the Connection tab, check mark ‘Connect to Microsoft Exchange Server using HTTP’ then press the ‘Exchange Proxy Settings’ button.
Finally this window appears. Fill it in exactly as shown match the image below, checking all boxes. Type or copy/paste in the first field, connect.emailsrvr.com, in the second msstd:connect.emailsrvr.com and select ‘Basic Authentication’.
Finish the process by pressing OK, OK, Next, Finish, then Close.
Close down then restart Outlook 2013 and the repair is complete.