Message and Recipient Limits
Applies to: Office 365 for professionals and small businesses, Office 365 for enterprises, Live@edu
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:
- Message limits
- Recipient and sender limits
- Retention limits
- Distribution group limits
- Transport rule limits
- Moderation limits
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, or 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. |
1,500 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 with Windows PowerShell.
| 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 |
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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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