prodigy.net rejected your message to the following email addresses

I received my last email via my att.net account on Tuesday, December 12, 2017, at 2:38 pm and have not received an email since.  When I send an email to my att.net email address from any other email address the email is returned as undeliverable and the following message appears: blank mailhost - invalid address, relay.  I spent three hours yesterday with AT&T technical support and they initially claimed that my account was working just fine but they refused to consider this message that any sender receives when attempting to email my att.net address.  I was given a fourth number to call to leave a voicemail message but I haven't received a response.  It's been two days now and I've received little effective support from AT&T for my paid email account I've had for twenty years.  What does a long-time paid customer have to do to get help from AT&T?

Wish I knew.  I have same issue.

Others are experiencing similar problems.  See

https://forums.att.com/t5/AT-T-Internet-Email-Security/Can-t-receive-email-incoming-email-bounces-with-quot-blank/m-p/5352321#M29288

I stopped receiving email to prodigy.net email address about Mid December. Have spent hours on the phone with AT&T, they are clueless.

After hours on the phone with ATT, and escalations, the solution is simple but not at all communicated by ATT.

Log into ATT.com with your legacy prodigy.net email address and use your current att.com password (for your other/main accounts. There you will be able to access a yahoo webmail account with your prodigy.net email. You can then set up a forwarder there to any other email addresses you want.