SMTP Code: 421 4.7.0 Too many concurrent connections

Products

• Messaging Gateway

Issue/Introduction

Messages are accumulating in the Messaging Gateway delivery queue for one or more domains with the SMTP status code:

421 4.7.0 Too many concurrent connections

Environment

Messaging Gateway

Cause

The destination mail server is rate limiting email delivery from Messaging Gateway by restricting the numbef of available SMTP connections.

Resolution

This issue cannot be addressed through Messaging Gateway configuration since the destination server is refusing / deferring SMTP connections from Messaging Gateway.

If the destination server in internal to your email environment please check it's configuration to ensure that it is not limiting SMTP connections from Messaging Gateway.