For bulk emails, you must also take care of certain restrictions on receiving and sending have been imposed to counteract spam, mass-mailing worms, or viruses. These limits play a crucial role in safeguarding system and ensuring the safety of the users. Check the below link for exchange limit, specially receiving and sending limits section. To adhere to these policies, it is essential to pay attention to the message rate limit, which is set at 30 messages per minute.
Exchange Online limits - Service Descriptions | Microsoft Learn[
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