I spent more than an hour on hold for tech support to resolve this 5.1.1 error message generated while trying to send out email, and all I finally was told is they are working on it. Now 30 hours later, it's still not working. Interesting that e-mail to a @cox.net account goes through, but all other non-Cox email recipients generate the message ("The server responded 5.1.1 <name> relaying not allowed. Please check the recipient and try again". Lousy service!! Until you can resolve this, 1) broadcast an e-mail message about the problem and the status of it's resolution, and 2) resume allowing SMTP port 25 and no password/authentication, and no SSL security, so your customers can at least send unsecured e-mails if they choose.
This is not too much to ask for the cost of our pricey Cox internet service!
Cwaters