How to block a user automatically if he sends more than 50 mails within 60 minutes

[Robert K]

How do I block a user automatically if he sends more than 50 mails within 60 minutes from his Exchange Online Account? The content (size, number of attachments, etc.) of the mail does not matter. The mail recipient or the type or location of the login (web, app, mobiles device) is also irrelevant. It is about the implementation of an internal compliance rule.

[#2]

You should be able to do that with a Cloud App Security activity policy, see https://support.office.com/en-us/article/Activity-policies-and-alerts-in-Office-365-Cloud-App-Securi... for the instructions.