Microsoft will soon begin throttling Exchange mailboxes Feb 23, 2021 02:18 EST · Hot! with 5 comments Microsoft's proprietary email hosting service Exchange Online - typically utilized by Outlook - has had an upper limit for emails received by "hot recipients" for quite some time. This term encompasses users who receive over 3,600 messages in their mailbox per hour. So far, this has been a soft-limit that Microsoft has not really enforced, but starting from April, this situation will change. Microsoft has stated that in order to optimize email flow across mailboxes and to ensure capacity across the Exchange services, it will begin enforcing its existing limit of being able to receive 3,600 messages per hour. The company says that when tenants and mailboxes go beyond this limit, services for other customers are disrupted as well, causing delays in emails being received due to network resources being utilized by "hot recipients".