Microsoft has started rolling out a ‘Reply All Storm Protection’ Exchange Online feature in Office 365 that helps avoid accidental mass replies in corporate emails. The feature’s first announcement was made back in Microsoft Ignite 2019.

“Initially the Reply All Storm Protection feature will mostly benefit large organizations who have large distribution lists. When the feature detects a likely reply all storm taking place on a large DL it will block subsequent attempts to reply all to the thread and will return an NDR to the sender. The reply all block will remain in place for several hours.”, explains Microsoft.

The feature kicks in when it detects 10 reply all-s involving over 5000 recipients within 60 minutes and will stay effective for 4 hours. Below is how the non-delivery report would look like when the feature gets triggered in the event of an email storm.

microsoft reply storm block example
Image: Microsoft

The feature will be initially limited to large organizations. However, the Redmond giant is working to expand it so that relatively smaller companies could get benefitted as well.“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.”, wrote Microsoft.

As pointed out by ZDNet, Microsoft got affected by two such incidents in the recent past, involving up to 52,000 employees in an email storm. The company says it has noticed reduced reply all storms internally ever since the first implementation of the feature.