A post from Office Support - https://support.microsoft.com/en-us/office/outlook-error-cannot-send-this-item-when-replying-to-an-e... describes an issue we are seeing where Outlook cannot reply to an email in a user's inbox. (Happens for multiple users in the company).
The article above was last updated October 6, 2021.
Can you please advise the current status of this issue?