Replying to emails from M365 Outlook group

Hi Mike Parker,

Thank you for posting your question in the Microsoft Q&A forum. 

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Yes, Microsoft 365 Groups are designed to allow members to reply from the group mailbox. By default, members can reply as themselves, and with the right permissions, they can also send as the group or on behalf of the group. These permissions need to be configured in Exchange Online. You can review and manage them in the Exchange Admin Center under Recipients > Groups > [Select Group] > Settings, where you will find the options for “Send As” and “Send on behalf.” More details are available in Microsoft’s documentation: https://free.blessedness.top/en-us/microsoft-365/solutions/allow-members-to-send-as-or-send-on-behalf-of-group?view=o365-worldwide.

Regarding the error message “This message can't be sent because it no longer exists,” from my research, this typically happens when the original message in the group mailbox is deleted or moved before the reply is sent. Outlook links the draft reply to the original message, so if that message is removed, the reply cannot be completed. If your workflow involves deleting emails after processing, this can cause the issue. A better approach is to use categories or flags to mark items as processed instead of deleting them immediately.

If some users still cannot reply even when the message is present, check for permission consistency across all members. Also, consider clearing cached email addresses, as outdated cache entries can cause sending failures. To do this, start a new email, type the address you want to clear (in this case, the recipient(s) in the message that could not be replied to), and when the suggestion appears, click the “X” to remove it, then retype the full address manually. In Outlook Web and the new Outlook, you can only remove entries individually. In classic Outlook Desktop, you can clear the entire Auto-Complete list under File > Options > Mail > Send messages > Empty Auto-Complete List.

I hope the information above helpful! If you have any further questions, please feel free to share.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".     

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.