SMTP Code: 554 5.1.2 Recipient address rejected: User unknown

Products

• Messaging Gateway

Issue/Introduction

Messages are being rejected by Messaging Gateway with the SMTP response code

554 5.1.2 Recipient address rejected: User unknown

Environment

Release : 10.9.0

Cause

The Inbound SMTP listener for Messaging Gateway is either

• Not configured to accept email for the recipient domain of the message or,
• Recipient validation for Inbound email has been configured and the recipient address for the email message does not match a valid recipient or domain in the Directory Data Source

In some cases, Outbound mail may be getting delivered to the Inbound SMTP listener on SMG resulting in a rejection of the messages. 

Resolution

1. Confirm that the messages are being delivered to the expected SMTP listener i.e. that an internal mail server is not attempting to deliver internet mail to the Inbound SMTP interface
2. Confirm that all local domains have been configured in Protocols > Domains
3. Confirm that recipient validation is operating as expected by testing known good addresses in Administration > Directory Integration > Data Source > Recipient Validation