In this post, let’s have a look at the error message “5.4.6 or 5.4.14 – Routing loop detected” 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.
5.4.6 or 5.4.14 – Routing loop detected
A configuration error has caused an email loop. 5.4.6 is generated by on-premises Exchange server (you’ll see this code in hybrid environments). 5.4.14 is generated by Exchange Online.
By default, after 20 iterations of an email loop, Exchange interrupts the loop and generates an NDR to the sender of the message.
This error occurs when the delivery of a message generates another message in response. That message then generates a third message, and the process is repeated, creating a loop. To help protect against exhausting system resources, Exchange interrupts the mail loop after 20 iterations. Mail loops are typically created because of a configuration error on the sending mail server, the receiving mail server, or both. Check the sender’s and the recipient’s mailbox rules configuration to determine whether automatic message forwarding is enabled.
For more information, see Fix email delivery issues for error code 5.4.6 or 5.4.14 in Exchange Online.