Exchange Online Sending and Receiving Limits

Microsoft do impose various limitations in Exchange Online and below are the limits defined for Sending and Receiving limits:

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

Receiving limits apply to the number of messages that an Exchange Online user, group, or public folder can receive.

• Receiving limit: This limit applies to the number of messages per hour from any and all sources. This includes messages from internal senders, messages from the internet, and messages from on-premises servers. When the receiving limit has been exceeded on a mailbox, messages sent to the mailbox will be returned to the sender in a non-delivery report (also known as an NDR or bounce message) stating that the mailbox has exceeded the maximum delivery threshold. After an hour, the limit will refresh and the mailbox will be able to receive messages.
• Sender-recipient pair limit: This limit applies to the number of messages per hour from a single sender. This is set to a ratio of the overall receiving limit to protect against single-sender mail storms.

RECEIVING LIMITS

Feature	Microsoft 365 Business Basic	Microsoft 365 Business Standard	Microsoft 365 Business Premium	Office 365 Enterprise E1	Office 365 Enterprise E3	Office 365 Enterprise E5	Office 365 Enterprise F3
Messages received	3,600 messages per hour	3,600 messages per hour	3,600 messages per hour	3,600 messages per hour	3,600 messages per hour	3600 messages per hour	3600 messages per hour
Messages received from single sender	33% of messages received	33% of messages received	33% of messages received	33% of messages received	33% of messages received	33% of messages received	33% of messages received

Sending limits

Sending limits apply to the number of recipients, number of messages, and number of recipients per message that a user can send from their Exchange Online account.

Note:

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, 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.

Note

Exchange Online customers who need to send legitimate bulk commercial email (for example, customer newsletters) should use third-party providers that specialize in these services.

Recipient limit: This is the maximum number of recipients allowed in the To:, Cc:, and Bcc: fields for a single email message.

Note

For the purposes of the recipient rate limit and the recipient limit, a distribution group that is stored in the organization's shared address book counts as one recipient. In a personal distribution list, each recipient is counted separately.

Recipient proxy address limit: The recipient proxy address limit is the maximum number of aliases (email addresses) that a recipient mailbox can have.

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.

 

SENDING LIMITS

Feature	Microsoft 365 Business Basic	Microsoft 365 Business Standard	Microsoft 365 Business Premium	Office 365 Enterprise E1	Office 365 Enterprise E3	Office 365 Enterprise E5	Office 365 Enterprise F3
Recipient rate limit1	10,000 recipients per day	10,000 recipients per day	10,000 recipients per day	10,000 recipients per day	10,000 recipients per day	10,000 recipients per day	10,000 recipients per day
Recipient limit2	Customizable up to 1000 recipients	Customizable up to 1000 recipients	Customizable up to 1000 recipients	Customizable up to 1000 recipients	Customizable up to 1000 recipients	Customizable up to 1000 recipients	Customizable up to 1000 recipients
Recipient proxy address limit	400	400	400	400	400	400	400
Message rate limit3	30 messages per minute	30 messages per minute	30 messages per minute	30 messages per minute	30 messages per minute	30 messages per minute	30 messages per minute

For more details and limitations, please refer to the below Microsoft documentation:

https://docs.microsoft.com/en-us/office365/servicedescriptions/exchange-online-service-description/exchange-online-limits#receiving-and-sending-limits