SMTP Error “421 4.3.2 Service not active”

Products

• Messaging Gateway

Issue/Introduction

Many messages are stuck in the delivery queue, showing the SMTP error:

421 4.3.2 Service not active

Cause

This error is returned by the next-hop MTA. It means the destination mail server is not accepting SMTP connections or its mail service is currently inactive.

Resolution

Contact the administrator of the next-hop MTA and verify:

• The SMTP service is running and active.

• The server is accepting connections from the SMG.

• No maintenance, outages, or configuration issues are preventing message relay.

Once the MTA is active and allowing connections, SMG will resume message delivery.