554 5.4.14 Hop count exceeded - Possible mail loop

Products

• Email Security.cloud

Issue/Introduction

The sender received a Non-Delivery Report (NDR) with the following error:

554 5.4.14 Hop count exceeded - possible mail loop [Additional server details provided by the Microsoft server]

Environment

Email Security.cloud

Cause

This error typically indicates a mail loop or routing issue in Exchange Online.

Resolution

To resolve this issue, follow these steps:

1. Analyze the email headers or routing path to identify the source of the loop.
2. Use the Track and Trace tool to check if multiple entries exist with the same Message-ID.
3. Verify if emails were redirected to ESS from Office 365, potentially creating a mail loop.

For more details, refer to the Microsoft article: Fix email delivery issues for error code 5.4.6 or 5.4.14 in Exchange Online KB