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Summary
This article covers two different types of sending limits which apply to all USNH email accounts. It is important to understand the difference because the steps required to restore sending capability depend on which limit was exceeded. This article applies to all users of USNH email accounts.
Overview
USNH email accounts are subject to two different types of sending limits:
While both are intended to protect users and the USNH email environment from spam, abuse, and compromised accounts, they behave differently and have different resolution processes.
Understanding the difference is important because the steps required to restore sending capability depend on which limit was exceeded.
See below for:
Who Is Affected?
This article applies to:
- Students
- Faculty
- Staff
- Retirees
- Alumni (where applicable)
using a USNH Microsoft 365 email account.
Sending Limits (set by USNH)
Sending limits are configured by USNH and control how many messages a user can send on a per hour and per day basis.
What Happens When a Sending Limit Is Reached?
When a sending limit is exceeded:
- The message that exceeds the limit cannot be sent.
- The user is temporarily prevented from sending additional email.
- The account is not considered compromised.
- The user is not placed on Microsoft's Restricted Senders list.
For example:
- A student sends emails to 250 different recipients within an hour.
- The student attempts to send an additional message.
- Sending is blocked until enough time has passed for the send count to fall back within the allowed limit.
USNH Sending Limits
| Account Type |
External per hour |
Internal per hour |
Per day |
| Alumni |
100 |
100 |
400 |
| Students |
250 |
250 |
1000 |
| Employees |
500 |
500 |
2,000 |
| Approved exceptions |
2,000 |
2,000 |
10,000 |
How Is Access Restored?
No action is required by IT.
The user simply needs to wait until the applicable time window (hourly or daily) expires.
Important
- Changing a password will not restore sending privileges when the limit has been exceeded.
- The only resolution is waiting for the applicable time period (hourly or daily) to pass.
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Rate Limits (set by Microsoft)
Microsoft enforces separate service-wide rate limits to protect Microsoft 365 from abuse and large-scale spam campaigns.
Examples of Microsoft rate limits include:
- Maximum emails sent per minute
- Maximum emails sent per day
At the time of publication, Microsoft enforces limits such as:
- Approximately 30 messages per minute
- Approximately 10,000 messages per day
These limits are controlled entirely by Microsoft and cannot be modified by USNH.
What Happens When a Rate Limit Is Reached?
Unlike USNH sending limits, exceeding a Microsoft rate limit can result in:
- The account being placed on Microsoft's Restricted Senders list.
- The user being unable to send email.
- Additional review being required before sending privileges are restored.
Microsoft treats this activity as potentially indicating:
- A compromised account
- Automated sending
- Spam activity
- Malware or bot activity
What Is the Restricted Senders List?
The Restricted Senders list is maintained by Microsoft.
Users on this list:
- Can continue to receive email.
- Cannot send email until the restriction is removed.
- May receive bounce-back messages indicating that sending has been blocked.
How can a User be Removed from the Restricted Senders List?
The fastest way to demonstrate that an account has not been compromised is typically to:
Step 1 - Change the account password.
Step 2 - Sign in again using the new password.
Step 3 - Contact the IT Service Desk if sending ability is not automatically restored within an hour.
Changing the password helps verify account ownership and reduces the likelihood that Microsoft continues to view the account as potentially compromised.
Important
- Password changes only help when the issue is related to Microsoft's Restricted Senders list.
- Password changes do not resolve USNH sending limit violations.
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Limits and Email Security
Distribution Lists and Rate Limits
Microsoft counts messages sent to distribution lists differently depending on the type of limit being evaluated. Together, these two limits help prevent compromised accounts from being used to distribute spam to large numbers of recipients.
For more details on distribution lists, see Outlook: Managing Email Distribution Groups
Microsoft Rate Limit Example
For Microsoft's rate limits:
- One email sent to a distribution list containing 1,000 members counts as one message.
This means distribution lists can significantly reduce the number of messages counted toward Microsoft's rate limits.
USNH Sending Limit Example
For USNH sending limits:
- One email sent to a distribution list containing 1,000 members counts as 1,000 emails.
This is one reason USNH maintains sending limits.
Together, USNH’s sending limits and Microsoft's rate limits help prevent compromised accounts from being used to distribute spam to large numbers of recipients.
Why Doesn't USNH Just Increase the Limits?
Email sending limits are an important security control.
The combination of:
- USNH sending limits, and
- Microsoft's rate limits
helps:
- Reduce spam
- Limit damage from compromised accounts
- Prevent automated abuse
- Protect USNH's email reputation
- Improve email deliverability for all users
Sending Mass Emails
Email accounts are intended for person-to-person and routine business communication.
If you need to send newsletters, marketing messages, event announcements, recruitment campaigns, or other large-scale communications, USNH recommends using a dedicated mass-mailing platform such as:
- Constant Contact
- Salesforce Marketing Cloud
- Other approved bulk-email services
These services are specifically designed for high-volume communications and provide better deliverability, unsubscribe management, and security compliance features.
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Frequently Asked Questions (FAQ)
Questions
Q1. I exceeded a USNH sending limit. Should I change my password?
Q2. I was placed on the Restricted Senders list. Should I change my password?
Q3. How can I tell which limit I exceeded?
Q4. Who should I contact if I need assistance?
Answers
A1. I exceeded a USNH sending limit. Should I change my password?
No. Password changes do not affect recipient limits.
You must wait for the applicable time window to expire before sending is restored.
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A2. I was placed on the Restricted Senders list. Should I change my password?
Yes. A password change is often the quickest way to demonstrate that your account has not been compromised and can help restore sending privileges.
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A3. How can I tell which limit I exceeded?
Generally:
- If sending resumes automatically after waiting for the hourly or daily window to expire, you likely exceeded a USNH sending limit.
- If you cannot send email and have been placed on Microsoft's Restricted Senders list, you likely exceeded a Microsoft rate limit or triggered Microsoft's anti-spam protections.
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A4. Who should I contact if I need assistance?
Contact the USNH Technology Help Desk if:
- You believe your account is incorrectly restricted.
- You have changed your password and still cannot send email.
- You need guidance regarding large-scale email communications.
Back to Questions
Further Readings
Outlook: Managing Email Distribution Groups
Outlook: USNH Email Account FAQ
Need additional help?
Submit an Email Services support request with as much detail as possible, or visit the Technology Help Desk Support page to locate your local campus contact information or to submit an online technology support request. For password issues you must call or visit the Help Desk in person.
For assistance concerning site creation, content sharing, file synchronization, or other common SharePoint, OneDrive, Teams, or Office app activities, we recommend our Microsoft 365 Learning sites:
Learn more about the great tools our Microsoft 365 Learning sites offer!