I have outlook 2007 andf when I try sending a message it just goes to
the out box but doesn't send. When I click on the send and receive
button it says 556 CLIENT AUTHENTICATION REQUIRED. USE ESMTP EHLO AND
AUTH.

Talk to your ISP/Mail Provider for the proper settings. Also try disabling
any Anti-Virus mail proxy that might be in the way.

--
-f.h.