In this article, we will review the case when the 'Unable to restore comments' error occurs on restoring data to Microsoft Planner.
Unable to restore comments: ErrorSendAsDenied: The user account which was used to submit this request does not have the right to send mail on behalf of the specified sending account., Cannot submit message.
This error occurs if the Planner account used for restoring data does not have an Exchange Online license. The Exchange Online license is required to be able to add task Comments. Microsoft Exchange Online is a hosted messaging solution that delivers email, calendar, contacts, and tasks from PCs, the web, and mobile devices, it is a part of the Microsoft 365 and Office 365 suite of products.
To find out if you have an Exchange Online license, open your mailbox, choose "File" and then click "Account Settings." In the dropdown menu, click "Account Settings." You'll see a summary of your configured email accounts with an indication of which ones are using Microsoft Exchange.
For more details about the account requirements for Planner data backup and restore please refer to the 'Connection account requirements' article.