Microsoft 365 Exchange Error Code 5.1.10 – Recipient not found

In this post, let’s have a look at the error message “5.1.10 – Recipient not found” that you get when working with Microsoft 365 Exchange Online.

These are the errors that you usually receive when there is a problem in delivering the email message that was sent by you. These errors are generated and sent by Office 365. This is usually alled as DSN which stands for delivery status notification or in simple words bounce messages.

NDR or Non-delivery report is one of the common type of message that you receive which indicates to the user that the email was not delivered.

Error Message

5.1.10 – Recipient not found

Error Details

The recipient’s wasn’t found by SMTP address lookup.

For more information, see Fix email delivery issues for error code 550 5.1.10 in Exchange Online.