Comcast Drops AT&T Domain?

We've heard through the grapevine that Comcast has permanently dropped the mail.attbi.com domain. We've not been able to confirm this. However, we have had several reports from customers that they are no longer able to send mail using the mail.attbi.com domain. Specifically, these customers have had to change their outgoing (SMTP) mail server from mail.attbi.com to smtp.comcast.net as per this FAQ.