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Microsoft rolls out protection against Office 365 email storms:
Microsoft is rolling out protection against Office 365 Reply-All email storms, an issue impacting Exchange Online users who are members of large and improperly locked down mail distribution lists.

Reply-All storms (also known as reply-allpocalypses) are huge chain reaction sequences of emails that start when a member of a large organization's email distribution list send a reply to all its members using the "Reply All" feature, in some cases effectively pinging the inboxes of thousands of people with a single mouse click.

A likely outcome of such an email storm is an inadvertent Distributed Denial of Service (DDoS) attack that would potentially take down one or all of the email servers that were used to deliver the tremendous amounts of replies exchanged.

Things get even more problematic when others use the "Reply All" feature, with tens if not hundreds of thousands of "email bombs" being delivered to all mailing list members for hours on end.
Reply All Storm Protection bounce message (aka NDR).jpg
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