If not, click the “Skip Get Started” button at the bottom-right of the screen you took your screenshot from. This will skip the wizard and take you to the Email Routing app.
From the Email Routing screen, select the “Destination addresses” tab and add/remove destination address(es) as desired.
After fixing the destination address, go to the “Routing rules” tab to create the custom address you started creating earlier and send it to the fixed email address.
Finally, click “Enable Email Routing” to create the necessary DNS records for Cloudflare Email Routing.
The error 521 5.3.0 Upstream error, please check Postmaster · Cloudflare Email Routing docs for possible reasons why. m7Gi7ya1Yc4x indicates that there’s an issue with delivering the email to the specified destination server. This is generally due to issue at the upstream mail server.
To address this concern, please reach out to destination mail server for further assistance. They will have necessary logs or relevant tools to further checking on the error delivery.