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Microsoft is saving you from Reply All hellstorms with this new Exchange feature

Microsoft is rolling out a new feature that will reduce the impact reply all storms have on organisations using Microsoft Exchange.

The feature, called Reply All Storm Protection, will primarily benefit large organisations with bigger distribution lists. The feature identifies incoming reply all storm conversations by detecting any 10 reply alls to over 5000 recipients in the space of 60 minutes.

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It will then temporarily block recipients from replying to the thread to avoid notifying every member of the conversation and overwhelming servers. Any person that attempts to reply to the thread will instead receive a bounce message, or NDR. The reply all block will remain active for four hours.

Screenshot of Microsoft about not being able to send the email conversation via reply all

Image: Microsoft

The company originally announced Reply All Storm Protection at Microsoft Ignite 2019 in November, citing the 1997 BedlamDL3 incident as inspiration for the new feature. BedlamDL3 saw one quarter of all Microsoft employees added to a distribution list, getting caught up in an email thread that generated 15 million messages, 195GB of data and slowed down Microsoft’s Exchange servers significantly.

“After the BedlamDL3 incident, the Exchange team introduced a number of features to help reduce the chance of such an occurrence from ever happening again, for Microsoft and for all Exchange customers”, explained Microsoft last November.

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“Hidden Distribution Lists, Recipient Limits, and DL sender restrictions were just a few of the measures introduced. And since then, the number of Reply-All storms and their severity have been greatly curtailed. Yet, human beings are. . .well, human. So people still get caught up in Reply-All storms, asking to be removed from a DL or to be removed from the thread that’s going on and on, etc”.

Reply All Storm Protection marks Microsoft’s latest attempt to limit the impact of this recurring issue. The new feature is currently rolling out to Office 365 users worldwide.

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