Microsoft 365 (M365) email accounts at CSU have specific limits on sending emails to maintain account security and prevent unauthorized mass messaging. These restrictions do not apply to CSU-specific distribution lists or mailing lists.
Applicable to: Fort Collins, Pueblo
Affiliation: Students, Faculty, Staff
Sending Limits
Message sending limits for Colorado State and CSU Pueblo Microsoft 365 (M365) email accounts:
- Maximum number of recipients in all emails sent in a 24-hour period:
- Students: 500 recipients per 24 hours
- Faculty and Staff: 2,000 recipients per 24 hours
-
Note: These limits will be reduced to 250 for students and 1,000 for faculty and staff at the end of June 2026.
- Maximum message size: 25 MB
- Maximum attachment size: 35 MB
- Maximum number of recipients in a single email: 500 recipients per email
Note: Sending emails to Exchange distribution lists is considered sending to a single recipient (i.e., if you send an email to a distribution list with 300 members, that counts as one recipient).
Details
- Increased phishing activity is the main use case of high-volume email, causing a growing negative impact on students, faculty, and staff. Limits prevent unauthorized mass emails in the event of account compromise, restricting potential impact and ensuring a suitable range for regular communications.
- Accounts that exceed the daily limit are blocked from further sending until reviewed and unblocked by the Division of IT.
- CSU defines a day as any rolling 24-hour period.
Recommended alternatives for sending large email distributions
CSU recognizes that there are legitimate business and academic needs to send emails to large audiences. To support these use cases while maintaining account security, CSU recommends using approved communication tools.
Using the appropriate method for high-volume or recurring email communications helps ensure reliable delivery and reduces the risk of account restrictions. For guidance on selecting the best option, see Mass email from Microsoft 365: Why you’re seeing blocks or throttling and better ways to send, which outlines recommended tools and scenarios for large-scale email messaging.
Outcome
By following these guidelines, CSU users can understand the email sending parameters, prevent accidental account restrictions, and manage large email distributions efficiently.