From April 2021, Exchange Online will apply hard limits for the number of messages a mailbox can receive per hour. The limit remains the same (3,600), but now Exchange will block the mailbox receiving any more email for an hour. The new version of the Exchange Admin Center (EAC) promises to highlight problem mailboxes so that admins can ask owners why their mailboxes receive so much email.
Many migration projects use Exchange Web Services (EWS) to move data to Exchange Online. EWS is using throttled to preserve resources. Here’s how to lift the restrictions for up to 90 days, all without going near a support call.