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452 5.5.3 - Too many recipients

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.

For billing and reporting purposes, and due to the way the 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.