We are currently tracking the issue on the virtual hosting email server related to an AT&T blacklist. Sample error:

—– Transcript of session follows —– … while talking to aln-mailrelay.att.net.:
>>> MAIL From: SIZE=22519
<<< 550-65.99.192.3 blocked by ldap:ou=rblmx,dc=worldnet,dc=att,dc=net
<<< 550 Blocked for abuse. See
http://www.att.net/general-info/rblinquiry.html
554 5.0.0 Service unavailable
… Deferred: Connection timed out with xyz

We have reported the issue to AT&T and are awaiting their response. According to their postmaster the response will be received within two days:

Thank you for submitting your inquiry. A response will be sent within two business days to the e-mail address you specified.

We’re sorry about the inconvenience and will update the ticket when the issue is resolved. Currently this is having a minimal impact to a single address on our virtual mail hosting network (if you absolutely must get the email through just try sending it again and it might hit a different gateway).

Update from AT&T at 4:30 PM EST:

Thank you for contacting the Postmaster/Abuse team at ATT.NET and BELLSOUTH.NET.

The mail-server IP address(es) associated with your request are NOT CURRENTLY BLOCKED from sending mail to any of our servers.  You may have received this message for any of the following reasons: the IP address you submitted has already been removed due to another request; the IP address you submitted is incorrect and the actual blocked IP address was not removed; the IP address you submitted has never been blocked at ATT.NET and BELLSOUTH.NET.  ATT.NET and BELLSOUTH.NET, its affiliates, and network services customers do NOT intentionally block legitimate mail in the course of our anti-spam initiatives.  We regret any inconvenience this may have caused.