Microsoft 365 Exchange Error Code 4.5.3 – Too many recipients

In this post, let’s have a look at the error message “4.5.3 – Too many recipients” that you get when working with Microsoft 365 Exchange Online.

These are the errors that you usually receive when there is a problem in delivering the email message that was sent by you. These errors are generated and sent by Office 365. This is usually alled as DSN which stands for delivery status notification or in simple words bounce messages.

NDR or Non-delivery report is one of the common type of message that you receive which indicates to the user that the email was not delivered.

Error Message

4.5.3 – Too many recipients

Error Details

The message has more than 200 SMTP envelope recipients from the same domain.

An envelope recipient is the original, unexpanded recipient that’s used in the RCPT TO command to transmit the message between SMTP servers. When this error is returned by Microsoft 365 or Office 365, the sending server must break up the number of envelope recipients into smaller chunks (chunking) and resend the message.