Bulk E-Mail and Daily Recipient Rate Limits

Article
07/03/2012

Applies to: Office 365 for professionals and small businesses, Office 365 for enterprises, Live@edu

There is a recipient rate limit, often called a sender limit or sending limit, for cloud-based e-mail accounts. This limit defines the maximum number of recipients that can receive e-mail messages sent from a single cloud-based account in a 24-hour period. The recipient rate limit for Exchange Online is 1,500 recipients per day.

The recipient rate limit applies to messages sent to recipients inside and outside your organization. After the limit has been reached, messages can’t be sent from the mailbox until the number of recipients that were sent messages in the past 24 hours drops below the limit. Multiple messages sent to the same recipient are counted separately. For example, if a user sends 10 messages to the same recipient in a 24-hour period, these 10 messages count as 10 recipients towards the recipient rate limit.

Important

The best way to avoid exceeding the recipient rate limit is to use distribution groups or dynamic distribution groups when you send messages to large numbers of recipients. Groups are counted as a single recipient toward the recipient rate limit. For example, if you send a message to 100 recipients by adding each of those recipients on the To:, Cc:, or Bcc: fields, that counts as 100 recipients toward the recipient rate limit. But if you add those same 100 recipients to a distribution group or dynamic distribution group, and then send the same message to the group, that counts as one recipient toward the recipient rate limit. See Strategies to support bulk e-mail.

Examples of the recipient rate limit

The recipient rate limit is based on a 24-hour rolling window. This means the recipient rate limit is calculated against the number of recipients that were sent a message in any 24-hour period. Here are examples to illustrate the recipient rate limit.

On a Monday morning, after not sending any e-mail over the weekend, you send a message to 1,500 recipients at 11:00 A.M. You can’t send another message until 11:00 A.M. the next day.
On another Monday morning, you send a message to 500 recipients at 9:00 A.M. You send another message to 500 recipients at 1:00 P.M. Then you send a third message to 500 recipients at 4 P.M. You can’t send another message until 9:00 A.M. the next day.
You haven't sent any messages in the last 24 hours, and then you send a message to one recipient at 7:30 A.M. You continue to send e-mail to lots of recipients during the day. If you send a message to the 1,500th recipient at 5:00 P.M., then you can’t send another message until 7:30 A.M. the next day.

Exchange Online also doesn’t accept a message for partial delivery to some recipients. If a user sends a message to multiple recipients, and the number of recipients for that message exceeds the recipient rate limit, the message is blocked for delivery to all recipients.

Why do we have this limit?

The recipient rate limit helps fight spam and prevent abuse by users inside your organization, hackers, or anyone using a hijacked account. The abuse of any account can affect the availability of your organization's service.

Microsoft provides additional protection, such as connection filtering and content filtering, for messages to cloud-based recipients. For more information, see Spam Filtering and Message Hygiene.

What happens when a mailbox exceeds the recipient rate limit?

Outlook Web App prevents the user from sending the message, and displays an error message in the information bar saying that the user has reached the recipient rate limit. The user can click Save to save the unsent message to the Drafts folder. When the mailbox is once again under the limit, the user can open the message in the Drafts folder and re-send it.

In Microsoft Outlook, the user can send the message. But the message is returned to the user with an error message saying that the message is undeliverable and couldn’t be sent. However, this non-deliverable message contains an option to send the message again. When the mailbox is under the limit, the user can click Send Again to resend the message.

What if I need to support bulk e-mail that exceeds the daily limit?

There are plenty of legitimate reasons for exceeding the recipient rate limit. For example, you may need to send a welcome message, billing statements, grades, or other uniquely addressed messages to many recipients at one time. Also, your organization may use automatic mailing applications that send e-mail messages in bulk, for example, library notifications for overdue books, announcements to customers, or sales advertisements. To send e-mail to large numbers of recipients, use any of the following strategies for sending large quantities of e-mail or sending e-mail to lots of recipients.

Strategies to support bulk e-mail

Let's look at the strategies for supporting the most common bulk e-mails scenarios.

Scenario	Examples	Solution
Broadcast messages Send the same message to a large number of users in your cloud-based organization.	Campus-wide announcements Messages to all employees from the CEO or other company officials	Use dynamic distribution groups Because a dynamic distribution group is counted as a single recipient, they'll help you stay under the sender limit. For more information, see Send Broadcast Messages to All Users. Use static distribution groups Regular distribution groups, also called public groups, are counted as a single recipient. Use a distribution group if the group membership won't change very much. Important For large distribution groups and dynamic distribution groups, make sure that you restrict who can send messages to the group or turn on message approval by a moderator. This will help prevent "reply-all storms" and spam sent to the group.
Bulk e-mail messages to cloud-based mailboxes Use mail merge or automatic mailing applications to send customized messages to uniquely addressed recipients in your cloud-based organization.	Library notifications Billing information for students Message from the CEO or other company officials	Use an on-premises mail server Configure automatic mailing or mail merge applications to use an on-premises server. You must add the IP addresses for on-premises servers to your safelists in the cloud. For more information, see Inbound Safe Listing Scenario.
Bulk e-mail messages to external mailboxes Use mail merge or automatic mailing applications to send customized messages to external users.	Welcome messages with sign-in credentials sent to new users Messages to alumni or parents Messages to existing or prospective customers Sales advertisements or special offers	Use an on-premises mail server Configure automatic mailing or applications to use an on-premises system. Use static or dynamic distribution groups Create external contacts for recipients such as parents, customers, or vendors, and then add external contacts as members of a static or dynamic distribution group.

Broadcast messages Send the same message to a large number of users in your cloud-based organization.

Campus-wide announcements
Messages to all employees from the CEO or other company officials

Use dynamic distribution groups Because a dynamic distribution group is counted as a single recipient, they'll help you stay under the sender limit. For more information, see Send Broadcast Messages to All Users.

Use static distribution groups Regular distribution groups, also called public groups, are counted as a single recipient. Use a distribution group if the group membership won't change very much.

Important For large distribution groups and dynamic distribution groups, make sure that you restrict who can send messages to the group or turn on message approval by a moderator. This will help prevent "reply-all storms" and spam sent to the group.

Bulk e-mail messages to cloud-based mailboxes Use mail merge or automatic mailing applications to send customized messages to uniquely addressed recipients in your cloud-based organization.

Library notifications
Billing information for students
Message from the CEO or other company officials

Use an on-premises mail server Configure automatic mailing or mail merge applications to use an on-premises server. You must add the IP addresses for on-premises servers to your safelists in the cloud. For more information, see Inbound Safe Listing Scenario.

Bulk e-mail messages to external mailboxes Use mail merge or automatic mailing applications to send customized messages to external users.

Welcome messages with sign-in credentials sent to new users
Messages to alumni or parents
Messages to existing or prospective customers
Sales advertisements or special offers

Use an on-premises mail server Configure automatic mailing or applications to use an on-premises system.

Use static or dynamic distribution groups Create external contacts for recipients such as parents, customers, or vendors, and then add external contacts as members of a static or dynamic distribution group.

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