In this post, let’s have a look at the error message “5.4.300 – Message expired” 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.
5.4.300 – Message expired
The email took too long to be successfully delivered, either because the destination server never responded or the sent message generated an NDR error and that NDR couldn’t be delivered to the original sender.