Verified with the admin that the server is actually available? They might be
doing some maintenance over the weekend.
The lack of detail in your post prevents us from giving us a more direct or
precise answer.
Include at least;
-your version of Outlook (Help-> About)
-type of mail account (POP3, IMAP, Exchange, HTTP, Outlook Connector,
Exchange, other...?)
-any errors in their exact wording as they are presented to you.
