Maximize Reply All Storm Protection: 4 PowerShell cmdlets for Microsoft Exchange Administrators

The reply-all function can be a blessing and a curse in any organization – great when it is used with the right recipients but nightmarish when it causes a reply-all storm in your organization that just won’t end.


Reply All Storms don’t just annoy users — they can generate a lot of unnecessary data and seriously disrupt productivity. The most common example of replies-gone-wrong is probably Microsoft’s self-dubbed Bedlam DL3, when a Reply All Storm ensnared over 25,000 people on a company distribution list. Members of the list kept replying to the thread (even replying to ask to be removed, which further spurred the issue), and ended up generating 15,000,000 email messages and 195 gigabytes of data.

In 2019– and in direct response to situations like Bedlam DL3– Microsoft announced the Reply All Storm Protection feature, which detected Exchange email threads where 10 reply alls to over 5000 recipients occurred within 60 minutes. The Reply All Storm Protection feature would then block subsequent replies to the thread for 4 hours.

Newly Expanded Options

Beginning May 2021 and fully available by mid-June, Exchange admins will have greater control over thresholds to detect and respond to reply all storms. The minimum number of recipients can be lowered to 1000, and block duration can extend from 1 to 12 hours, for example.

SettingCustomizable options
Enabled/disabledEnabled or Disabled
Minimum number of recipients1000 to 5000
Minimum number of reply-alls5 to 20
Detection time sliding window60 minutes (not customizable)
Block duration (once detected)1 to 12 hours
Chart of expanded customizations for each setting

PowerShell Cmdlets

For now, admins can use PowerShell cmdlets to update the settings for their organization though the Exchange Transport Team has expressed interest in hearing feedback about making this available in the Exchange Admin Center. Also in that post, the team mentions plans to provide insights, reports, and optional notifications for the Reply All Storm Protection feature in the future.

SettingPowerShell cmdlet
Enabled/disabledSet-TransportConfig -ReplyAllStormProtectionEnabled [$True:$False] 
Number of recipients thresholdSet-TransportConfig  -ReplyAllStormDetectionMinimumRecipients [1000 – 5000]
Number of reply-alls thresholdSet-TransportConfig -ReplyAllStormDetectionMinimumReplies [5 – 20]
Block durationSet-TransportConfig -ReplyAllStormBlockDuration [1 – 12]
Chart of Powershell cmdlets to update Reply All Storm Protection settings

As a reminder Microsoft is moving away from using UserVoice in favor of 1st party feedback solutions, but there are a number of other ways to leave your feedback directly.

Thanks for reading, we hope you’ll check out the other posts on our blog and visit our site to learn more about our services and the nonprofits and social impact small businesses we serve.

Microsoft 365 Roadmap ID 68840
Exchange: Update to Exchange Online Reply-All Storm Protection (MC254418)
Prevent Users from Using Reply, Reply All, Forward, Print, or Attach

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