Update 5/5/2021: For additional information on this subject and new settings, please see this post.
When a reply all mail storm happens in your organization, it can disrupt business continuity and ...
Updated May 05, 2021
Version 3.0
Blog Post
KevinShaughnessy
Microsoft
MicrosoftM_Durbs - I'm not on the Outlook team but I believe this IRM capability would address your point about "Do Not Reply All" in Outlook, no? https://support.microsoft.com/en-us/office/preventing-reply-all-433041fe-0475-405a-b579-ddddf4951481?ui=en-us&rs=en-us&ad=us
Jan_Rademan - this only applies to mailboxes in Office 365.
maheshsingh_it - technically it's actually based on the number of fully expanded recipients, not based on the size of the DL. So you could have 100 DLs of 50 recipients each + 1 lone recipient and the fully expanded recipient count would be 5001. Such a thread would qualify because total recipients are > 5000. For simplicity the post describes the common scenario, rather than describing the underpinning technical mechanisms. We'll consider creating a technically oriented KB article in the near future.
BruceRoberts - Thanks for the input on the NDR text. I can see the headline ". . .too busy. . ." could use some work. I think the other elements will likely be understandable, e.g. "Do not use Reply All," and "Don't resend the mail" but we'll take another look at the whole thing. That said, in practice, understanding the NDR won't matter much - we'll still stop the reply-all storm whether people understand the NDR or not. 🙂