Office 365 Email Receiving and Sending Limits


Each Office 365 Outlook user is able to send one email to 500 recipients at a time per hour and can send to 5,000 recipients per day. These settings are not changeable per Microsoft's Email Policy. The definitions of the different limitations are explained in detail below, along with our policy if blocked for spamming by Microsoft. 

More Information

  • Sending email with large email attachment. There is a 150 MB file size limit for both incoming or outgoing Emails.  This is the total size of the email, not just the attachment. The size restriction is for Faculty, Staff and Student email accounts.
    • If the attachment is larger than 150 MB, it can be broken down into multiple parts and sent separately
    • Not receiving an Email with a large attachment? Contact the sender and ask if the attachment can be broken into smaller attachments and sent separately.


Sending limits

Sending limits apply to the number of recipients per day, 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 the Contacts folder of a mailbox, the members of the group are still 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 in total each day

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 per hour.

Note: In a personal distribution list, each recipient is still counted separately.

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 overconsumption 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.


Feature Office 365 
Recipient limit (per hour) 500 recipients
Recipient rate limit (per day) 5,000 recipients per day
Message rate limit (SMTP client submission only)

30 messages per minute

Blocked for spamming

Violating the email limit can result in Microsoft blocking your account from sending emails. You will get a message like below:  

"Delivery has failed to these recipients or groups:
Your message couldn't be delivered because you weren't recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it's no longer allowed to send email. Contact your email admin for assistance."

if you violate this policy more than once then your email privileges will be suspended for 24 hours. it is recommended to use mail merge to avoid being blocked by Microsoft for spamming. Click here for instructions from Microsoft's site on mail merge.


Article ID: 81586
Mon 6/24/19 4:27 PM
Fri 8/4/23 9:52 AM