Microsoft rolls out its Reply All Storm Protection feature to Office365 worldwide

Hemani Sheth Mumbai | Updated on May 11, 2020 Published on May 11, 2020


Microsoft on Sunday announced that it will be rolling out its Reply All Storm Protection feature for Office 365 worldwide.

The feature had been announced back in 2019 at Microsoft’s Microsoft Ignite 2019 event. It is an attempt to stop a storm of e-mails when recipients, part of a large conversation click on ‘reply all’ for emails marked with a huge number of people. The feature is meant to put a temporary reply-all email block in place to prevent a system overload due to a reply all ‘storm.’

“When a ‘reply all mail storm’ happens in your organisation, it can disrupt business continuity and in some cases even throttle the rest of your organisation’s email for a period of time,” Microsoft explained in an official blog post.

A major example of how these ‘reply all emails’ can disrupt business continuity is the Bedlam DL3 incident. Back in 1997.

In 1997 a Microsoft employee noticed that he was on a distribution list (DL) called BedlamDL3. He sent an email to be removed from the list not realizing that the DL included one-quarter of all Microsoft employees, around 13,000 members at that time who all received a copy of his request to be removed from the DL. Other employees also started to use Reply All to also ask to be removed. Within an hour 15 million messages were generated amounting to 195 GB of data bringing Microsoft's Exchange servers to a slow crawl. It had taken two days to clean up the servers.

After the BedlamDL3 incident, the Exchange team had introduced a number of features to prevent such instances including Hidden Distribution Lists, Recipient Limits, and DL sender restrictions were just a few of the measures introduced.

Most recently in March, thousands of Microsoft employees were included in another reply-all email thread that had been shut down in 30 minutes, The Verge reported.

The feature is to further prevent reply-all threads with a large number of employees and maintain business continuity.

Microsoft will put the feature in place when it detects 10 reply all-s to over 5,000 recipients within 60 minutes. It will then block subsequent replies to the thread for 4 hours.

“We’ll maintain the temporary block (and sending of NDRs) active for a number of hours, a ‘cool-down’ period, to let the storm pass so people can get back to their regular work,” Microsoft explained.

“Over time, as we gather usage telemetry and customer feedback, we expect to tweak, fine-tune, and enhance the Reply All Storm Protection feature to make it even more valuable to a broader range of Office 365 customers,” it further said.

Published on May 11, 2020

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