@William Thank you for reaching out to Microsoft Q&A. Apologize for the inconvenience caused on this.
As per the current limitation you can only send 25 emails per subscription in 60 Minutes period of time as mentioned in the documentation here.
Sending a high volume of messages has a set of limitations on the number of email messages you can send. If you hit these limits, your messages won't be queued to be sent. You can submit these requests again, once the Retry-After time expires.
WorkAround : I would suggest you Submit a support request with the below details to raise your desired sending limit if you require sending a volume of messages exceeding the rate limits.
- Domain currently sending email from?
- Platform currently used?
- IP address (if available)?
- Expected Daily/Monthly Volume?
- Type of emails sent (Transactional/Marketing/Promotional)?
- Source of the Email addresses list?
- Process to cleanup the list of Unsubscribe/Bounces?
Please do let us know if you need any further assistance required while raising the support ticket.