smtp/pop3 service configuration

[neologos]

I put in place a smtp/pop3 service in a windows 2003 environment, but
sending an email from to a test email I have the following error:

Delivery to the following recipients failed.

testmail5@xxxxxxxxx.com



Reporting-MTA: dns;xxxxxxxxserver

Arrival-Date: Sun, 19 Feb 2006 18:28:51 +0100

Final-Recipient: rfc822;testmail5@mail.xxxxxx.com
Action: failed
Status: 5.3.5

status indicates a configuration error but I do not KNOW what it is-
Help!! :->