Emails from Microsoft Office 365 are being rejected by Symantec Email Security.Cloud

Products

• Email Security.cloud

Issue/Introduction

Error Message:
Symantec Email Security.Cloud is rejecting outbound emails from Microsoft 365 with the following message:

Error:
[ {LED=453-you are trying to use me [server-X.tower-XXX.messagelabs.com] as a relay, but I have not been configured to let you [40.XX.XX.XX, mail-domain_name.outbound.protection.outlook.com] do this. Please visit https://knowledge.broadcom.com/external/article?legacyId=TECH246726 for more details about this error message and instructions to resolve this issue. (#4.7.1)}; {MSG=}; {FQDN=mailXXX.messagelabs.com}; {IP=XX.XXX.XXX.XXX}

Environment

Symantec Email Security.Cloud 

Microsoft Office 365

Cause

Outbound email traffic from Microsoft 365 is being sent through the High-Risk Delivery Pool IPs, which are not registered or authorised in the Symantec Email Security.Cloud platform.

Microsoft may reroute outbound mail through this pool under certain conditions (e.g., spam risk mitigation). These IPs fall outside the standard Microsoft 365 ranges and require special configuration.

Reference:

 

• About the High-Risk Delivery Pool – Microsoft

• Broadcom Article – Relay Configuration Error

 

Resolution

To authorise emails from the Microsoft 365 High-Risk Delivery Pool, follow these steps:

1. Navigate to the Dashboard > Platform > Outbound Routes section in the Symantec Email Security.Cloud portal.

2. Under Hosted Email Services, select Microsoft Office 365 High-Risk Delivery Pool from the dropdown.

3. Click Add.

This action will authorize and add all relevant Microsoft 365 High-Risk Delivery Pool IP addresses to your outbound configuration, allowing mail to relay successfully through Symantec infrastructure.