Q. What is the sending limit when sending a large number of emails using THERS email?
A. The maximum number of recipients you can send emails to per day is 10,000.
In addition, the maximum number of messages that can be sent per minute is 30. When sending emails to multiple recipients using CC or BCC, the total number of recipients (including TO, CC, and BCC) must not exceed 500 per message.
If you exceed 10,000 recipients, a sending restriction will be applied. This restriction cannot be lifted by the administrator, so you will need to wait until it is automatically lifted, which may take up to 24 hours.
Reference: Exchange Online limits | Sending limits