DRAFT: Exchange Online Limits

Find the Exchange Online limits for a variety of service areas, including address book limits, mailbox storage limits, and reporting and message trace limits, to name just a few.

The limits in Microsoft Exchange Online fall into one of the following categories:

• Address book limits

• Mailbox storage limits

• Capacity alerts

• Mailbox folder limits

• Message limits

• Receiving and sending limits

• Reporting and message trace limits

• Retention limits

• Distribution group limits

• Journal, Transport, and Inbox rule limits

• Moderation limits

• Exchange ActiveSync limits

Address book limits

• Address list limit The maximum number of address lists that can be created in an Exchange Online or Exchange Server 2013 organization. This number includes the default address lists in Exchange Online, such as All Contacts and All Groups.

• Offline address book limit The maximum number of offline address books (OAB) that can be created in an Exchange Online or Exchange Server 2013 organization.

• Address book policies limit The maximum number of address book policies (ABP) that be created in an Exchange Online or Exchange Server 2013 organization.

• Global address lists The maximum number of global address lists (GAL) that be created in an Exchange Online or Exchange Server 2013 organization.

Address book limits across Office 365 options

Address book limits across standalone plans

Mailbox storage limits

The amount of mailbox storage available is determined by the mailbox type and the user’s subscription license. Administrators can reduce maximum mailbox sizes per user or globally.

Storage limits across Office 365 options

Storage limits across standalone plans

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Capacity alerts

Exchange Online provides three kinds of notifications when a user’s mailbox is nearing, or at, capacity:

• Warning   The user receives an email warning that the mailbox is approaching the maximum size limit. This warning is intended to encourage users to delete unwanted mail.

• Prohibit Send   The user receives a prohibit-send notification email when the mailbox size limit is reached. The user cannot send new messages until enough email is deleted to bring the mailbox below the size limit.

• Prohibit Send/Receive   Exchange Online rejects any incoming mail when the mailbox size limit is reached, and sends a non-delivery report (NDR) to the sender. The sender has the option to try resending the mail later. To receive messages again, the user must delete email until the mailbox is below the size limit.

Capacity alerts across Office 365 options

Capacity alerts across standalone plans

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Mailbox folder limits

These limits are intended to limit mailboxes to known dimensions that can be supported in Exchange Online. The goal of these limits is to prevent an infinite number of mailbox items per folder, an infinite number of folders per mailbox, or an infinite number of public folders per Exchange Online organization. For practical purposes, mailbox folder limits are in effect unlimited and sufficient to support most Exchange Online mailboxes and on-premises mailboxes that are migrated to Exchange Online.

• Maximum number of messages per mailbox folder   Specifies the maximum number of messages for a mailbox folder. New messages can’t be delivered or saved to a folder when this limit is reached.

• Warning for number of messages per mailbox folder   Specifies the number of messages that a mailbox folder can hold before Exchange Online sends a warning message to the mailbox owner. When this quota is reached, warning messages are sent once a day.

• Maximum number of messages per folder in the Recoverable Items folder   Specifies the maximum number of messages that can be contained in each folder in the Recoverable Items folder. When a folder exceeds this limit, it can’t store new messages. For example, if the Deletions folder in the Recoverable Items folder has exceeded the message count limit and the mailbox owner attempts to permanently delete items from their mailbox, the deletion will fail.

• Warning for number of messages per folder in the Recoverable Items folder   Specifies the number of messages that each folder in the Recoverable Items folder can hold before Exchange Online logs an event to the application event log.

• Maximum number of subfolders per mailbox folder   Specifies the maximum number of subfolders that can be created in a mailbox folder. The mailbox owner won’t be able to create a new subfolder when this limit is reached.

• Warning for number of subfolders per mailbox folder   Specifies the number of subfolders that can be created in a mailbox folder before Exchange Online sends a warning message to the mailbox owner. When this quota is reached, warning messages are sent once a day.

• Maximum folder hierarchy depth   Specifies the maximum number of levels in the folder hierarchy of a mailbox. The mailbox owner won’t be able to create another level in the folder hierarchy of the mailbox folder when this limit is reached.

• Warning for folder hierarchy depth   Specifies the number of levels in the folder hierarchy of a mailbox folder that can be created before Exchange Online sends a warning message to the mailbox owner. When this quota is reached, warning messages are sent once a day.

• Maximum number of public folders   Specifies the maximum number of public folders in the complete public folder hierarchy. When this limit is reached, existing public folders must be deleted before new public folders can be created.

• Maximum number of subfolders per public folder   Specifies the maximum number of subfolders that can be created in a public folder. New subfolders can’t be created in a public folder when this limit is reached.

• Warning for number of subfolders per public folder   Specifies the number of subfolders that can be created in a public folder before Exchange Online sends a warning message to the folder owner. If no owner exists, warning messages are sent to users with Owner permissions. When this quota is reached, warning messages are sent once a day.

Mailbox folder limits across Office 365 options

Mailbox folder limits across standalone plans

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Message limits

The following limits are applied to every email message.

• Message size limit   Message size limits are necessary to prevent large messages from blocking delivery of other messages and affecting service performance for all users. These limits include attachments, and apply organization-wide to all messages (inbound, outbound, and internal). Messages larger than this limit will not be delivered, and the sender will receive a non-delivery report (NDR). While message size limits can be configured up, down, or on a per-user basis, administrators can also create transport rules to limit the maximum size of any individual attachment. To learn more, see Office 365 now supports larger email messages.

  注意

  Particular email clients may have lower message size limits or may limit the size of an individual file attachment to a value that is less than the Exchange Online message size limit.

• Subject length limit   The maximum number of text characters allowed in the subject line of an email message.

• File attachments limit   The maximum number of file attachments allowed in an email 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. This limit is controlled by the multipart message limit.

• File attachment size limit   The maximum file size of a single attachment.

  注意

  This is the maximum file size of a single attachment. Individual client programs, including Outlook Web App, may limit the size of attachments below this maximum. Exchange ActiveSync does not implement attachment size limits on an individual attachment basis. The total size of all attachments to an Exchange ActiveSync message must be less than the message size limit.

• Multipart message limit   The maximum number of message body parts that are allowed in a MIME multipart message. This limit also controls the maximum number of file attachments that are allowed in a message.

• Embedded message depth limit   The maximum number of forwarded email messages that are allowed in an email message.

Message limits across Office 365 options

Message limits across standalone options

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Receiving and sending limits

Receiving and sending limits are applied to combat spam and mass-mailing worms or viruses. These limits help to protect the health of our systems and keep our users safe.

Receiving limits

Receiving limits apply to the number of messages that a user, group, or public folder can receive per hour. This applies for both messages received from the Internet and from on-premises servers. When the receiving limit has been exceeded, any emails sent to that mailbox will receive a non-delivery report stating that the mailbox has exceeded the maximum delivery threshold. After one hour, the limit will refresh and the mailbox will once again be able to receive messages.

Sending limits

Sending limits apply to the number of recipients, number of messages, and number of recipients per message that a user can send from their Exchange Online account.

• Recipient rate limit   To discourage the delivery of unsolicited bulk messages, Exchange Online has recipient limits that prevent users and applications from sending large volumes of email. These limits are applied per-user to all outbound and internal messages.

  注意

  Exchange Online customers who need to send legitimate bulk commercial email (for example, customer newsletters) should use third-party providers that specialize in these services.

• Recipient limit   This is the maximum number of recipients allowed in the To:, Cc:, and Bcc: fields for a single email message.

  注意

  For the purposes of the recipient rate limit and the recipient limit, a distribution group that is stored in the organization's shared address book counts as one recipient. In a personal distribution list, each recipient is counted separately.

• Message rate limit   Message rate limits determine how many messages a user can send from their Exchange Online account within a specified period of time. This limit helps prevent overconsumption of system resources by a single sender. If a user submits messages at a rate that exceeds the limit via SMTP client submission, the messages will be rejected and the client will need to retry.

Sending limits across Office 365 options

Sending limits across standalone options

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Reporting and message trace limits

For reporting and message trace limits, see the “Reporting and message trace data availability and latency” section in Reporting and Message Trace in Exchange Online Protection.

Retention limits

These limits control the length of time that items in specific folders in the Inbox can be accessed.

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

• 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’re permanently deleted.

• Junk Email folder retention period   The maximum number of days that items can remain in the Junk Email folder before they’re automatically removed.

Retention limits across Office 365 options

Retention limits across standalone options

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Distribution group limits

These limits apply to distribution groups in your organization's shared address book.

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

• 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.

• 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.

Distribution group limits across Office 365 options

Distribution group limits across standalone options

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Journal, Transport, and Inbox rule limits

The following list includes limits that apply to journal rules, transport rules (also known as organization-wide rules), and limits that apply to Inbox rules. Inbox rules are set up by individual users and applied to messages sent and received by the individual user’s mailbox.

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

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

• 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.

• 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.

• Scanning limits for attachment content The transport rule conditions enable you to examine the content of message attachments, but only the first 1 MB of the text extracted from an attachment is inspected. This 1 MB limit refers to the text extracted from the attachment, not to the file size of the attachment. For example, a 2 MB file may contain less than 1 MB of text, so all of the text would be inspected

• 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.

• 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.

• 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.

Journal, Transport, and Inbox rule limits across Office 365 options

Journal, Transport, and Inbox rule limits across standalone options

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Moderation limits

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

• 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).

• Maximum number of moderators   The maximum number of 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.

• 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.

• 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 receive notification messages for moderated messages that have expired. However, these notifications are still discoverable using delivery reports.

Moderation limits across Office 365 options

Moderation limits across standalone options

Exchange ActiveSync limits

The following limits apply to Microsoft Exchange ActiveSync, a client protocol that synchronizes mailbox data between mobile devices and Exchange.

• Exchange ActiveSync device limit   The maximum number of Exchange ActiveSync devices per mailbox.

• Exchange ActiveSync device deletion limit   The maximum number of Exchange ActiveSync devices that an Exchange administrator can delete in a single month.

• Exchange ActiveSync file attachment limit   The maximum size of a message file attachment that can be sent or received by an Exchange ActiveSync device.

Exchange ActiveSync limits across Office 365 options

Exchange ActiveSync limits across standalone options

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