Microsoft to Crackdown on High Volume Microsoft 365 Email Offenders

If your organization has mailboxes that are overflowing with data and you have been ignoring the warnings that they have surpassed the receiving limits for the account, you will need to start paying more attention. Microsoft has announced that it will be strictly enforcing limits across all mailboxes to protect the health of its system.

Starting in April, Microsoft will begin to enforce a limit of 3600 messages per hour to a recipient (MC239262). If you surpass this threshold, the company states that they will throttle messages to the account.

The fact that the company is making this a hard limit, previously it was a soft cap, means they must be seeing challenges from specific accounts. Because of this, you will need to take action if you have a mailbox surpassing this message-per-hour rate.

And you might be thinking, “how will I know if I have an account that is going to be hit by this new ceiling?” Even though Microsoft says that there are only a small number of accounts that will be impacted, they have created a new alert called “Mailbox exceeding receiving limits” insight and report in the Exchange Admin Center that will generate a notification if one or more accounts meets this threshold.

If you navigate to and see the following text, “Some mailboxes need attention: one or more mailboxes have exceeded their receiving limits” – then you need to take action.

Thinking a bit more logically, receiving more than 3600 emails per hour is significant and likely indicates that the inbox is the dumping-ground for some sort of automated action. While there are potentially public-facing email addresses, like a “contact us” that could hit this volume, it would seem more logical that a company is using a mailbox for reporting of transactional information and sending it to an inbox.

If this is you, then you are going to need to find a new path for monitoring the health of whatever system is tied to that mailbox. Previously, I have seen instances where a client will have a status email sent to an inbox and then have a rule set up for the word “fail” and only when that word is detected, to fire off an alert which means the thousands of other emails are simply noise. This is one example of how someone could be surpassing the 3600 limit.

All this being said, starting in April Microsoft is going to get serious about imposing the 3600 rate limit, if you think you have an account close to or exceeding that rate, you need to act now to mitigate the offending account from facing potential disruption in a few weeks.