In this post, let’s have a look at the error message “5.7.124 – Sender not in allowed-senders list” 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.
5.7.124 – Sender not in allowed-senders list
The sender doesn’t have permission to send to the distribution group because the sender isn’t in the group’s allowed-senders list. Depending how the group is set up, even the group’s owner might need to be added to the allowed sender list in order to send messages to the group.
For more information, see Fix email delivery issues for error code 5.7.124 in Exchange Online.