With the increase in teleworking, the load that the mail servers bear also increases. And old customs also come back, like email bombing. Microsoft announces that it has released new functionality that blocks group emails that are sent with the Reply to all options. This block will be used with emails transmitted through Office 365 and Exchange online.
In a company, it is common to create mailing lists for all employees, which are sometimes made up of thousands of users. The correct thing to do when sending an email to the entire list is to do it with the With Hidden Copy option, which prevents users from having access to the rest of the emails on the list.
But if due to an error, because it has never been done, or because the mailing list is incorrectly configured, an email is sent to hundreds or thousands of people without a blind copy, if each user responds to the email with the Reply to all option, It sends its mail to thousands of people, and those thousands, in turn, respond to thousands of people, causing what is called a storm or email blitz.
One of the most famous happened to Microsoft itself in 1997, in what is known as the Bedland DL3 incident.
Someone had created a mailing list called Badland DL3 with the emails of 25,000 Microsoft employees. When those employees received a message from the list, they didn’t know why they were on it, so many responded to the email asking what they were doing there… with the Reply All button. In just a few minutes, 15 million messages were generated, occupying 195 GB of data, blocking Microsoft’s Exchange mail servers.
In recent months, with the rise of teleworking, mailing lists have returned, and Microsoft has already detected numerous email bombings, even within the company itself. So you have decided to block the Reply all option in Office 365 and Exchange Online. When someone uses it with large mailing lists, this message will appear:
After the crash, the popup advises a reply to the email using Send to a single recipient, or to a smaller group.
Microsoft ensures that this block will only be activated at the moment when it detects the sending of 10 messages with Reply to all within a list of 5,000 or more participants, within 60 minutes. Over time, you plan to fine-tune the system so that it does not harm users.