If you are an Exchange or Office 365 Administrator, it is likely that you have seen Outlook Connectivity issues at some point; including Outlook remaining disconnected, repeatedly prompting for credentials, or users unable to create a new profile in Outlook to connect to their mailbox on Office 365.
Our support teams receive calls on this topic quite frequently, and have put together an excellent Office 365 Outlook Connectivity troubleshooter to walk you through identifying and resolving connectivity problems.
Make sure to bookmark the troubleshooter at: http://aka.ms/outlookconnectivity. and keep an eye on the excellent Office 365 support wiki topic Fix Outlook connection problems after Office 365 upgrade.
h/t to: http://community.office365.com/en-us/blogs/office_365_technical_blog/archive/2013/06/24/outlook-connectivity-troubleshooting-guided-walkthrough.aspx