Email Routing: 521 550 Upstream error. b2v5EmAvTMMj

Hi, i created 2 email in Email Routing. one work full but when i send email to other remail i get below error:

Address not found

Your message wasn’t delivered to redacted because the domain redacted couldn’t be found. Check for typos or unnecessary spaces and try again.

The response from the remote server was:
521 550 Upstream error. b2v5EmAvTMMj

Could you please share the domain you are using? @sven2

it is sibdiet.com. i had to disable email routing.

I am having the same issue (Email routing error 521 Upstream error) with the domain bakerandhamilton.com