Technical Guide: Resolving the Error 554 5.7.1 : Relay access denied
As the Microsoft 365 Administrator, encountering the 554 5.7.1 : Relay access denied error when sending to an external domain indicates a breakdown in the trust relationship between your MS365 tenant and the recipient’s mail server. The “Relay access denied” error is a permanent SMTP rejection. It means the recipient’s mail server received your email […]