Email beta feedback

I have a couple of domains in the email beta preview, both had DNS auto setup about a week ago.
1 domain is fowarding emails as expected.

1 of the domains bonces back and email with the following error message
(have sent 2 test emails days apart)

The response from the remote server was:

451 4.3.0 Configuration error

I wonder if it has anything to do with this issue that was fixed earlier:

Could you please share the domain you are using? (here or privately at sven (at) cloudflare).