Microsoft will add Reply-All protection to Office 365

Microsoft will add Reply-All protection to Office 365

Microsoft plans to add mass-mail protection with Reply-All Reply-All enabled in Office 365. The corporation’s employees themselves fell victim to it in January of this year.



Typically, such a mailing list (also called reply-allpocalypse) begins with the fact that one of the members of the large email list responds using the "Reply to All" function. As a result, an unintended DDoS attack can occur that can potentially lead to the failure of one or more email servers.

“When Reply-All happens in your organization, it can disrupt the continuity of business processes and even cause an unexpected restriction on the organization’s activities,” Microsoft said.

The company explained that Exchange Online already has several features designed to prevent reply-allpocalypse, for example, allowed-sender lists and recipient lists (DL), but this does not completely solve the problem.

Microsoft will add Reply-All protection to Office 365


The new protection, which is planned to be introduced in the third quarter of 2020, determines when Reply-All occurs or can potentially occur, and automatically blocks the possibility of a response for the corresponding users for a limited period of time. During this period, the email service will deliver a non-delivery message (NDR).

“The temporary block will be active for several hours, usually enough to weaken the flow of responses, and thus reduce the scale of reply-allpocalypse,” adds the development team.

At the same time, work is underway on a feature with which mail servers will see emails protected by Office 365 message encryption service, which makes them less likely to be marked as spam and sent to the Trash folder. The function is planned to be introduced around January 2020.

In addition, Microsoft is working to create a feature called “Unconfirmed Sender” that should help users identify potentially unwanted or phishing messages that fall into their Outlook client’s mailbox.

More than 11 thousand Microsoft employees on January 24 of this year were drawn into the mass mailing list, the participants of which had the “reply to all” function. It began with a letter from an employee associated with a company’s account on GitHub, which included instructions on how to receive fewer notifications from GitHub.

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