Error: 451 4.4.2 [internal] connection closed by remote host in Email Security Cloud

Products

• Email Security.cloud

Issue/Introduction

Emails remain in the delivery queue with a status of "retrying delivery." After several attempts, the delivery fails with a transient error. This issue occurs when the Email Security Service (ESS) attempts to deliver a message to the recipient mail server, but the connection is terminated prematurely.

Track and Trace logs shows the error as  :
451 4.4.2 [internal] connection closed by remote host

Environment

Email Security.cloud

Resolution

This is not an issue with the Email Security Service, as the service is actively attempting to deliver the message.

Please contact the recipient domain administrator for the root cause.