What is the name of the domain?
What is the error number?
What is the error message?
521 5.3.0 Upstream error, please check Postmaster | Cloudflare Email Routing docs for possible reasons why. IY4odZHnc57i
What is the issue you’re encountering
Problem with receiving mails
What are the steps to reproduce the issue?
Error receiving mails from Gmail forwarded from my domain to outlook com