Message and Recipient Limits

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

Topic last modified: 2014-01-31

After you enroll your organization, users may have the following questions that directly affect their e-mail experience:

  • Are any sending size limits applied to e-mail messages?

  • What recipient limits are applied to e-mail messages?

The limits on messages, mailboxes, recipients, and e-mail clients fall into one of the following categories:

Important   Be aware of the following:

  • The limits applied to your domain may differ depending on how long your domain has been enrolled in the service. When a limit is changed in the Microsoft datacenters, it can take some time to apply the change to all existing customers.

  • You can't modify most of these limits, but you and your users should be aware of them.

  • These limits apply to both internal and external recipients.

Message limits

These limits are applied to every e-mail message.


Limit Value

Message size limit   The maximum total size of an e-mail message. The total size includes the message header, the message body, and any file attachments.

Note   An e-mail client may limit the size of an individual file attachment to a value much less than the message size limit. For example, in Outlook Web App, the maximum individual file attachment size is 10 MB.

25 MB

File attachments limit   The maximum number of file attachments allowed in an e-mail message. Even if the total size of all the file attachments doesn't violate the message size limit, there is still a limit on how many attachments are allowed in the message.

125 attachments

Subject length limit   The maximum number of text characters allowed in the subject line of an e-mail message.

255 characters

Multipart message limit   The maximum number of message body parts that are allowed in a MIME multipart message.

250 parts

Embedded message depth limit   The maximum number of forwarded e-mail messages that are allowed in an e-mail message.

30 embedded messages

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Recipient and sender limits

These limits are applied to messages, senders, and recipients to combat spam and mass-mailing worms or viruses.

Note   For distribution groups stored in the shared 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.


Limit Value

Recipient limit   The maximum number of message recipients allowed in the To, Cc, and Bcc fields.

500 recipients

Message rate limit   The maximum number of e-mail messages that can be sent from a single e-mail client per minute. The client is identified by the user account.

30 messages per minute

Recipient rate limit   The maximum number of recipients that can receive e-mail messages sent from a single cloud-based mailbox in a 24 hour period. 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. The recipient rate limit applies to messages sent to recipients inside and outside your organization. For more information, see Bulk E-Mail and Daily Recipient Rate Limits.

  • Microsoft Live@edu: 1,500 recipients per day*

  • Office 365 for professionals and small businesses: 10,000 recipients per day

  • Office 365 for enterprises: 10,000 recipients per day

Forwardee Limit The maximum number of recipients that can be configured for an inbox or transport rule with a redirecting action. If a rule is configured to redirect a message to more than this number of recipients, the rule won't be applied and any message that satisfies the rule condition won't be redirected to any of the recipients listed in the rule.

10 recipients

* When a Microsoft Live@edu organization is upgraded to Office 365 for Education, the recipient rate limit is increased to 10,000 recipients per day.

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Retention limits

These limits control the amount of time that items in specific folders in the Inbox are accessible.

You can change these values by modifying the corresponding retention policy tags. For more information, see Set Up and Manage Retention Policies in Exchange Online.


Limit Value

Deleted Items folder retention period   The maximum number of days that items can remain in the Deleted Items folder before they are automatically removed.

30 days

Retention period for items removed from the Deleted Items folder   The maximum numbers of days that items removed from the Deleted Items folder are retained before they are permanently deleted.

14 days

Junk E-mail folder retention period   The maximum number of days that items can remain in the Junk E-mail folder before they are automatically removed.

30 days

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Distribution group limits

These limits apply to distribution groups.


Limit Value

Maximum number of distribution group members   The total recipient count is determined after distribution group expansion.

100,000 members

Limit sending messages to large distribution groups   Distribution groups that contain the number of members specified by this limit must have delivery management or message approval options configured. Delivery management specifies a list of senders who are allowed to send messages to the distribution group. Message approval specifies one or more moderators who must approve all messages sent to the distribution group. For more information, see Change Distribution Group Properties.

5,000 or more members

Maximum message size for large distribution groups   If a message is sent to 5,000 or more recipients, the message size can't exceed this limit. If the message size exceeds the limit, the message isn't delivered, and the sender receives a non-delivery report (NDR). The total recipient count is determined after distribution group expansion.

2 MB

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Transport rule limits

These limits control organization-wide rules, also known as transport rules.


Limit Value

Maximum number of transport rules   The maximum number of rules that can exist in the organization.

100 rules

Maximum size of an individual transport rule   The maximum number of characters that can be used in a single transport rule. The characters are used in the conditions, exceptions, and actions.

4,000 characters

Character limit for all regular expressions used in all transport rules   The total number of characters used by all the regular expressions in all the transport rule conditions and exceptions in the organization. You can have a few rules that use long and complex regular expressions, or you can have many rules that use simple regular expressions.

20,000 characters

Maximum number of recipients added to a message by all transport rules   When a message is acted on by different transport rules, only a finite number of recipients can be added to the message. After the limit is reached, any remaining recipients aren't added to the message. Also, distribution groups can't be added to a message by a transport rule.

100 recipients

Number of times a message is redirected   The number of times a message will be redirected, forwarded, or replied to automatically based on Inbox rules. For example, User A has an Inbox rule that redirects messages to User B, based on the sender. User B has an Inbox rule that forwards messages to User C based on keywords in the subject line. If a message satisfies both of these conditions, the message is only sent to User B; it’s not forwarded to User C because only one redirection is allowed. In this case, the message is dropped without sending a non-delivery report (NDR) to User B indicating that the message wasn’t delivered to User C. Similarly, if User B has configured an Automatic Reply (also known as an Out of Office message), a message that is redirected or forwarded to User B will not generate an auto-reply.

This limit prevents e-mail loops that can result in filling up a user’s mailbox to its maximum capacity.

1 redirection

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Moderation limits

These limits control moderation settings used for message approval applied to distribution groups and transport rules.


Limit Value

Maximum size of the arbitration mailbox   If the arbitration mailbox exceeds this limit, messages that require moderation are returned to the sender in a non-delivery report (NDR).

10 GB

Maximum number of moderators   The maximum number moderators that you can assign to a single moderated distribution group or that can be added to a message using a single transport rule. Note that you can't specify a distribution group as a moderator.

10 moderators

Expiration for messages waiting for moderation   By default, a message waiting for moderation expires after two days. However, the processing of expired moderated messages runs every seven days. This means that a moderated message can expire at any time between two and nine days.

2 days

Maximum rate for expired moderation notification messages   This limit sets the maximum number of notification messages for expired moderated messages in a one hour period. This limit is placed on each mailbox database in the datacenter.

During periods of heavy usage, some senders may not get notification messages for moderated messages that have expired. However, these notifications are still discoverable using delivery reports.

300 expiration notifications per hour

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