Can't receive email - incoming email bounces with "blank mailhost - invalid address" error
As of the evening 12/12/2017 (Eastern Time US), some ameritech.net domain email addresses began to experience an inability to receive new emails - though the ability to send remains intact. Incoming emails bounce with a "blank mailhost - invalid address" error.
POP3 mail is used; the error is independent of the sending browser or domain.
Further, the problem has "spread" over time, affecting some ameritech.net email addresses on the evening of 12/12/2017, and others the afternoon of 12/13/2017. Still other ameritech.net addresses remain unaffected.
A 2.5 hour phone call with ATT Support resulted finally in an admission that there was an "outage", and that the ability to receive emails would be restored within 72 hours. However, the above symptoms do not square with an isolated single IMAP server interruption.
Any advice or suggestions on how to solve this problem are appreciated.