Augie Grayfox wrote:
> How the HELL is sending an email from my @cox address to my client's @xxx.com 
> address be considered relaying?
> I thought that was just emailing somebody?

I reread your original email and have a few questions:

1. Is it only not allowing to this particular email address?
2. Have you sent to this email address previously, successfully?
3. Have you changed any SMTP settings that might cause it now to fail?

I know when I was setting up my FreeBSD box to act as a central mail 
server (relaying up to smtp.west.cox.net) I ended up having to use a 
valid domain name before the cox server would accept my connection. 
However, if your able to send to others and just not this particular 
account, that doesn't seem to be a similar issue.