To fix “Target Principal Name is Incorrect” error please configure your outlook's outgoing and incoming mail server to use webhosting2.a1whs.com instead of mail.yourdomain.com .
This applies to those using IMAP and are getting the above error message, no need to re-configure your outlook.
Also the above fix is only in one location, nothing else needs to be changed for your outlook configuration.
See this image : http://www.a1whs.com/randomimages/server-information-outlook.jpg for what fields that need to be changed.
