Receiving and sending limits are applied to combat spam and mass-mailing worms or viruses. These limits help to protect the health of our systems and keep our users safe.
Receiving limits apply to the number of messages that a user, group, or public folder can receive per hour. This applies for both messages received from the Internet and from on-premises servers. When the receiving limit has been exceeded, any emails sent to that mailbox will receive a non-delivery report stating that the mailbox has exceeded the maximum delivery threshold. After one hour, the limit will refresh and the mailbox will once again be able to receive messages.
Messages received limit 3,600 messages per hour
Sending limits apply to the number of recipients, number of messages, and number of recipients per message that a user can send from their Microsoft office 365 email (Exchange Online) account.
For distribution groups stored in an organization's address book, the group is counted as one recipient. For distribution groups stored in the Contacts folder of a mailbox, the members of the group are counted individually.
Recipient rate limit To discourage the delivery of unsolicited bulk messages, Microsoft office 365 email (Exchange Online) has recipient limits that prevent users and applications from sending large volumes of email. These limits are applied per-user to all outbound and internal messages.
Recipient limit This is the maximum number of recipients allowed in the To:, Cc:, and Bcc: fields for a single email message.
Message rate limit Message rate limits determine how many messages a user can send from their Exchange Online account within a specified period of time. This limit helps prevent over consumption of system resources by a single sender. If a user submits messages at a rate that exceeds the limit via SMTP client submission, the messages will be rejected and the client will need to retry.
Recipient rate limit 10,000 recipients per day
Recipient limit 500 recipients per message
Message rate limit (SMTP client submission only) 30 messages per minute
For more information on limits see here
Additional resources to help you make the most of Office 365
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