Error sending an email "452 too many recipients (#4.5.3)"

Products

• Email Security.cloud

Issue/Introduction

An external user is sending hundred of emails to recipients utilizing Email Security.cloud

OR 

An Email Security,cloud user is sending an external emails and getting the error below :

452 (#4.5.3) too many recipients 

Environment

Email Security.Cloud

Cause

The email is being sent out to more than 500 recipients in a single SMTP transaction. For a single SMTP transaction, the number of recipients in the RCPT TO command must not exceed to 500. 

Resolution

Configure your mail server to send to a maximum of 500 recipients for a single SMTP transaction.