2 weeks ago my site was using Exchange 2007.
I went on vacation and as part of a planned migration another team updated my site to Exchange 2010. Upon returning I found problems with the web mail server which is hosted at another site and my site has been having issues getting to our mailboxes via OWA. Once I moved the mailboxes in question back to the original server users were able to get OWA and the Outlook client worked.
Any ideas on what I should check would be appreciated.