What is the name of the domain?
What is the error number?
Deferred: 421
What is the error message?
Deferred: 421 att-e2xms-ibgw-6001a.ext.cloudfilter.net cmsmtp 209.235.146.243 blocked AUP#CNCT
What is the issue you’re encountering
After attempt to sending the email to Cloudflare customer, our customer got bounce back mentioned above.