Are you getting the error message "None of the authentication methods supported by this client are supported by your server" when using Outlook?
Users are beginning to see this message more often due to recent internet standards changing to make servers more secure by default. If you want to get geeky and see the technical reason, you can review here (http://en.wikipedia.org/wiki/SMTP_AUTH) and here (http://docs.cpanel.net/twiki/bin/view/AllDocumentation/WHMDocs/RequireSMTP).
Fixing this is easy. In your Outlook Account Settings, go into MORE SETTINGS -> OUTGOING SERVER and enable
"My outgoing server (SMTP) requires authentication"
Here is a link to a page outlining this in detail for Outlook 2010.