Can't use Reply All in email messages in Microsoft 365 groups

Last Updated: November 14, 2025

ISSUE

Consider the following scenario:

You're a member of a Microsoft 365 group.
You receive an email message that's addressed to the group, and you want to respond to the message.

You take the following actions:

In Outlook on the web or new Outlook, go to the navigation bar, select Groups, and then select your group name from the list.
Select the email message.
Select Reply all.
Enter your response, and then select Send.

In this scenario, you receive the following error message:

"Couldn't send this message."

If you select the More details link, you get the following information:

This message can't be sent because it no longer exists. It can only be discarded. Make sure you copy the contents of the message before you discard if you want to use them later.

STATUS: INVESTIGATING

Microsoft is researching this problem and will post more information in this article when it becomes available.

WORKAROUND

To work around this issue, use Reply instead of Reply All.