Forum Discussion
521 5.2.1 Error: True source IP is in global black list
Hello Everyone, I am new to the Exchange Online and recently we have migrated our service from G suite to Office 365 and since we migrated we are getting an error "521 5.2.1 Error: True source IP...
Is the error for outbound or inbound mail?
- For outbound - When we send an email to the recipient we get the above error as bounce back.
