Mail send problems since cpanel update

[nsusa]

I update my server to

WHM 10.8.0 cPanel 10.9.0-C56
RedHat Enterprise 4 i686 - WHM X v3.1.0

and since then I am having problems sending emails. Get the following error:


Your message did not reach some or all of the intended recipients.

Subject: Time expiration
Sent: 10/27/2006 10:27 PM

The following recipient(s) could not be reached:

'[email protected]' on 10/27/2006 10:27 PM
500 unrecognized command

The messages get rejected immediately from my server.

Any idea of why this would be happening after the udate?

Chris