Again 521 5.3.0 Upstream error

It seems that after first setup of Email Beta - for catch-all address there is some error.
It looks the same as in:

The specific addresses works crrectly - not sure about catch-all one…

Some message:

Status: 5.3.0
Remote-MTA: dns;
Diagnostic-Code: smtp; 521 5.3.0 Upstream error. 5jvzKYghrqab

I have a similar issue with the error message
but cannot post here as it said “Sorry, new users can only put 4 links in a post.”

Hey! I am also facing the same error.

Facing the same issue. Anyone get help from support or any other info to diagnose the underlying issue?