In this post, let’s have a look at the error message “5.7.503 – Access denied, banned sender” 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.
5.7.503 – Access denied, banned sender
The sending account has been banned due to detected spam activity.
Verify that any account issues have been resolved, and reset its credentials. To restore this account’s ability to send mail, please contact support through your regular channel.