Using Classic Outlook on Windows for personal email, calendar, and contact management
Dear Kyle_wb11,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Based on your description, I understand that you have a concern with 'Reply All prompt on M365 Outlook client'.
After thorough research and consulting, I found that the currents Outlook 365 doesn't have this feature built-in to prompt users asking if they are sure to reply all, and I know there was a macro that can be used or an add-in like Reply To all Monitor that work with Outlook 2010, or ReplyAll that work with outlook 2000 to outlook 2013, however, currently no add-in feature to do the same in outlook 365.
We apologize if we are not able to meet your requirements; however, thank you for bringing this to our attention, we will surely raise you concerns to our Product Team and hopefully this can be included in the future updates. Moreover, I would like to invite community members and MVPs in the forum to share their knowledge or any workaround and insight on this topic.
For other concerns, please do not hesitate to add you post in the Microsoft Community Team.
Thank you for your cooperation and understanding.
Sincerely,
De Paul | Microsoft Community Moderator