We need a lot more info than that. What happens if you send an e-mail to
yourself? Any error message? Post it. You can left click on it to highlight
and then right click to copy and then paste it into this thread.

What anti-virus program do you use? If you have e-mail scanning enabled,
turn it off.

By Server, I presume that you mean you called your ISP and they blamed
Outlook Express.

Are you getting any error message when you try Send and Receive?

The full text of the error message would be helpful.  That includes the
server name, server type, port number, socket error code, SSL, etc.  For
best results, copy/paste the error message rather than retyping it.  You
should be able to highlight the message text in the error window (hold
down the left mouse button while dragging the mouse over the text).
Then press Ctrl-C (hold down the Ctrl key while pressing the C key) to
copy the highlighted text to the Windows clipboard.  You can then paste
that text into the problem description using the Ctrl-V key combination.

Were things working fine before you installed SP3?

How to troubleshoot error messages that you receive when try to send and
receive e-mail in Outlook and in Outlook Express
http://support.microsoft.com/?kbid=813514

No server ever says that.  Stop trying to summarize or paraphrase an
error message.  Copy it verbatim.

Not with the dearth of information you have provided so far.

There is no version 2005 of Windows XP.  There is no 2005 version of
Microsoft Office XP.

What has SP-3 got to do with your problem?  Are you implying rather than
actually stating that the installation of SP-3 caused your e-mail
problem?

How to post to newsgroups:
http://66.39.69.143/goodpost.htm
http://support.microsoft.com/kb/555375
http://users.tpg.com.au/bzyhjr/liszt.html