Today I have created a demo tenant to test Microsoft Planner features and logged-in to the Planner Portal with a test account and tried to post a comment in a Planner task, the comment was placed successfully but it was reverted immediately and the comment removed with some unknown technical error.
Actually a Planner plan’s comments feature is connected with its associated group’s conversation (Modern Office 365 Group Conversation). So I have tried to check the problematic plan’s group conversation is really works or not by clicking triple-dots (…) >> Conversation.
But I received the below error while accessing a group conversation page.
:-( Something went wrong We couldn’t find a mailbox for this recipient. Either they don’t have a mailbox or don’t have a license assigned. X-OWA-Error: Microsoft.Exchange.Clients.Owa2.Server.Core.OwaUserHasNoMailboxAndNoLicenseAssignedException
Solution
As I already said the Planner comments feature is powered by Office 365 Groups conversation, so to enable this feature your tenant should have Exchange Online license first and the user who is trying to post a comment should have valid Exchange Online license. In my case, the user account doesn’t have a license and the problem was solved after assigning the license.
Without Exchange Online license you can’t use this feature as of now. You can’t use On-Premise Exchange service since the modern unified group conversation is supported only through Exchange Online mailbox.
You may still face issue to post comment (and error something like below while accessing conversation page) after assigning Exchange Online license but if the mailbox was not created for the user.
:-( Something went wrong A mailbox couldn't be found for [email protected]. X-OWA-Error Microsoft.Exchange.Data.Storage.UserHasNoMailboxException
When a new Office 365 account is granted an exchange online license, it might take few moments for the mailbox provision. The maximum wait time is 48 hours.
Please try logging in OWA (https://outlook.office.com/owa/) later to see if the issue persists.
You can also change to another browser and use the incognito or private mode to check if there are any improvements.
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