452 5.5.3 - Too many recipients

In order to ensure the best performance in mail delivery for all of our customers, our servers are configured to allow a maximum of 500 recipients in each message.  This includes any recipients in the TO, CC, and BCC fields of your message.

If you need to send a message to more than 500 recipients, it is recommend that you use software that will automatically send each as a separate message or break up your list of recipients to sets of 500 or less; Please be aware that for billing and reporting purposes, and due to the way SMTP protocol works, if you send a message with 500 recipients, we will count that as 500 messages sent because we must send a separate individual message to each recipient you have chosen to list.