In this article

• Address book limits
• Capacity alerts
• Distribution group limits
• Dynamic distribution group limits
• Exchange ActiveSync limits
• Hold limits
• Journal, transport, and inbox rule limits
• Mailbox folder limits
• Mailbox storage limits
• Message limits
• Moderation limits
• Receiving and sending limits
• Reporting and message trace limits
• Retention limits

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

Note
If you need assistance with a task or if you are troubleshooting a problem, you might find the following articles helpful:

• Email (for help creating and sending email)
• Email in Microsoft 365 for business – Admin Help
• Fix Outlook and Microsoft 365 problems with Microsoft Support and Recovery Assistant
• Email non-delivery reports
• Exchange Online Help

Exchange Online limits fit into one of the following categories:

• Address book limits
• Capacity alerts
• Distribution group limits
• Dynamic distribution group limits
• Exchange ActiveSync limits
• Hold limits
• Journal, transport, and inbox rule limits
• Mailbox folder limits
• Mailbox storage limits
• Message limits
• Moderation limits
• Receiving and sending limits
• Reporting and message trace limits
• Retention limits

Important

• The limits applied to a Microsoft 365 organization may differ depending on how long the organization has been enrolled in the service.
• When a limit is changed in the Microsoft data centers, 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.
• By default, Exchange Online Protection (EOP) protects Exchange Online mailboxes. For limits that apply to EOP features in Exchange Online, see Exchange Online Protection limits.
• For information about Office 365 group limits, see How do I manage my groups? in Learn about Microsoft 365 groups.
• Storage allocations in Education tenants may be limited. Please see Office 365 Education service description for details.

Address book limits

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

Note
A maximum of 20 address lists can be assigned to a single offline address book (OAB). The maximum size of a single offline address book is 1GB.

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

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

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

Address book limits

Address book limits across standalone plans

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 can’t 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 can try resending the mail later. To receive messages again, the user must delete email until the mailbox is below the size limit.

Capacity alerts

Capacity alerts across standalone plans

¹ This is the default value for Exchange Server organizations. Administrators can change this value for their organization.

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.
• 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 an NDR.

Distribution group limits

¹ If you’re using Microsoft Entra DirSync, the maximum number of distribution group members that you can synchronize from your on-premises Active Directory to Microsoft Entra ID is 15,000. If you’re using Microsoft Entra Connect, that number is 250,000, but the supported limit of distribution group members is still 100,000.
² This limit also applies to admins.

Distribution group limits across standalone options

¹ This is the default limit for Exchange Server organizations. Administrators can change this value for their organization.
² This limit also applies to admins.

Dynamic distribution group limits

Dynamic distribution group limit: The maximum number of dynamic distribution groups (DDGs) that can be created in an Exchange Online or Exchange Server organization.

Dynamic distribution group limits

Dynamic distribution group 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 limits

Exchange ActiveSync limits across standalone options

Hold limits

Holds include Microsoft 365 retention policies and retention label policies, Microsoft Purview eDiscovery case holds, and In-Place Holds. These count towards the 10,000 per tenant maximum for compliancy policies that also include policies for Microsoft Purview Data Loss Prevention, Microsoft Purview Information Barriers, and sensitivity labels.

Note
Exchange retention policies from messaging records management (MRM) are excluded from this 10,000 maximum.

• Maximum number of Microsoft 365 retention policies per tenant: 1,800
• Maximum number of holds per mailbox: 25 is the recommended maximum before performance might be impacted; 50 is the supported limit.

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. Individual users can set up inbox rules that are applied to messages sent and received by the individual user’s mailbox.

• Maximum number of journal rules
• Maximum number of transport rules
• Maximum size of an individual transport rule
• Character limit for the sum of all regular expressions
• Scanning limits for attachment content
• Maximum number of recipients added to a message by all transport rules
• Forwardee limit
• Number of times a message is redirected
• Number of times a message is redirected by transport rules

Journal, transport, and inbox rule limits

¹ If a mailbox was migrated to Exchange Online, the inbox rule limit might be set to a value that is lower than the default EXO value. If that is the case, the inbox rule value can be increased. For instructions, see Modify the space used by Inbox rules in Exchange Online.

Journal, transport, and inbox rule limits across standalone options

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.

• Maximum number of messages per mailbox folder
• Warning for number of messages per mailbox folder
• Maximum number of messages per folder in the Recoverable Items folder
• Warning for number of messages per folder in the Recoverable Items folder
• Maximum number of subfolders per mailbox folder
• Warning for number of subfolders per mailbox folder
• Maximum folder hierarchy depth
• Warning for folder hierarchy depth
• Maximum number of public folders
• Maximum number of subfolders per public folder
• Warning for number of subfolders per public folder

Mailbox folder limits

¹ This is the storage quota for the Recoverable Items folder, not the quota for the entire archive mailbox. The storage quota for the archive mailbox is 1.5 TB for users with an Exchange Online Plan 2 license or for users who have both an Exchange Online Plan 1 and an Exchange Online Archiving license. For information about increasing the Recoverable Items quota, see Increase the Recoverable Items quota for mailboxes on hold.
² The initial storage quota for the Recoverable Items folder in an archive mailbox is 100 GB. When auto-expanding archiving is turned on, additional storage is automatically added when the storage capacity for the Recoverable Items folder is reached. For more information, see Overview of auto-expanding archiving.
³ This is a store limit; it’s one of the mailbox shape constraints. There can be only 10,000 direct child folders for any given parent.

Mailbox folder limits across standalone plans

¹ Microsoft recommends no more than 1,000,000 messages per mailbox folder.
² If the auto-expanding archive isn’t enabled, this space is the storage quota for the Recoverable Items folder, not the quota for the entire archive mailbox.
³ The initial storage quota for the Recoverable Items folder in an archive mailbox is 100 GB, after which auto-expanding archiving adds additional storage.

Mailbox storage limits

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

Note
Using journaling, transport rules, or auto-forwarding rules to copy messages to an Exchange Online mailbox for the purposes of archiving is not permitted. A user’s archive mailbox is intended for just that user. Microsoft reserves the right to deny additional archive storage space in instances where a user’s archive mailbox is used to store archive data for other users or in other cases of inappropriate use.

Storage limits

¹ Each user initially receives 100 GB of storage in the archive mailbox. When auto-expanding archiving is turned on, additional storage is automatically added until the archive reaches 1.5 TB.
² To access a shared mailbox, a user must have an Exchange Online license, but the shared mailbox itself doesn’t require a separate license (up to 50 GB). Above 50 GB or for advanced features, additional licensing may be required.
³ Resource mailboxes don’t require a license. However, they’re limited to 50 GB unless assigned an E3 or E5 license, which increases the limit to 100 GB.
⁴ Archive mailboxes aren’t included in Exchange Online Kiosk.
⁵ The default individual public folder size limit is 2GB (which can be changed). Maximum recommended size of individual public folder is 25 GB.
⁶ You’re limited to 1,000 public folder mailboxes, and the maximum total size of all public folder mailboxes is 100 TB.
⁷ Archive mailboxes can only be used to archive mail for a single user or entity (license required).
⁸ If you created a retention policy in Exchange Online, messages are automatically moved to a user’s archive mailbox only if the user’s primary mailbox is larger than 10 MB.
⁹ Assigning an E3 or E5 license to a shared/resource mailbox can increase size to 100 GB.
¹⁰ Shared mailboxes have a system-generated active user account (unknown password). To block sign-in, see Block sign-in for the shared mailbox account.

Storage limits across standalone plans

¹ This is the default mailbox size for Exchange Server organizations; administrators can change it.
² Auto-expanding archiving: additional storage is added when the 100 GB limit is reached, up to 1.5 TB total.
³ A user license is required to access a shared mailbox. Shared mailboxes are limited to 50 GB unless assigned Exchange Online Plan 2 or Plan 1 + Archiving.
⁴ Resource mailboxes don’t require a license, but remain at 50 GB unless assigned Plan 2 (100 GB).
⁵ Archive mailboxes can be purchased as an add-on through Exchange Online Archiving.
⁶ Default is 2 GB for on-premises; can be changed. On-premises is limited to 100 public folder mailboxes total.
⁷ In Exchange Online, you’re limited to 1,000 public folder mailboxes, up to 50 TB total.
⁸ Archive mailboxes must only store mail for the single user/entity licensed.
⁹ Retention policies only move items to the archive mailbox if the primary mailbox is larger than 10 MB.
¹⁰ Assigning a Plan 2 license or Plan 1 + Archiving license lets you enable advanced features, including additional storage for the mailbox or placing the mailbox on litigation hold.
¹¹ Shared mailboxes have an associated active user account with a system-generated password. See Block sign-in for the shared mailbox account.

Message limits

The following limits are applied to every email message.

• Message size limit
• Message header size limit
• Subject length limit
• File attachments limit
• File attachment size limit
• Multipart message limit
• Embedded message depth limit

Message limits

¹ The default maximum message size is 35 MB for sending and 36 MB for receiving. Admins can specify a limit up to 150 MB.
² You can send and receive up to 150 MB messages between users within Microsoft datacenters. Internet-bound messages have an additional 33% overhead.
³ OWA restricts to 25% less than the configured size to allow for overhead.
⁴ The size for move-based migrations is computed by Exchange Online.
⁵ For info on OME with new capabilities, see Set up new Message Encryption capabilities.
⁶ Classic file attachments have a limit of 112 MB; OneDrive file attachments can be up to 2 GB.

Message limits across standalone options

¹² Admins can specify a custom limit (1–150 MB).
¹³ OWA accounts for 33% overhead, thus 25% reduction.
⁴ This is the default for on-premises Exchange; can be changed.
⁵ Size for move-based migrations is computed by Exchange Online.
⁶ Set up new Message Encryption capabilities.

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
• Maximum number of moderators
• Expiration for messages waiting for moderation
• Maximum rate for expired moderation notification messages

Moderation limits

Moderation limits across standalone options

¹ This is the default limit for Exchange Server organizations. Administrators can change this value.

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 an Exchange Online user, group, or public folder can receive.

• Receiving limit: The maximum number of messages per hour from any and all sources.
• Sender-recipient pair limit: The maximum number of messages per hour from a single sender.

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
• Recipient limit
• Recipient proxy address limit
• Message rate limit
• Tenant External Recipient Rate Limit (TERRL)

¹ After the recipient rate limit is reached (10,000), messages can’t be sent until the count in the past 24 hours drops below the limit.
² You can customize recipient limits between 1 and 1000.
³ Based on total characters; ~300 addresses recommended.
⁴ Exceeding this throttles the user’s message submission.
⁵ Length of the email addresses + the encryption policy can’t exceed 4 MB.

Sending limits across standalone options

¹ Default for Exchange Server can be changed by admins.
² After 10,000 recipients in 24 hours, you must wait until that count drops below 10,000 to send more mail.

Sending and receiving meeting invite limits

Recipient limits for meeting invitations or updates is 5,000 recipients per meeting message.

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
• Retention period for items removed from the Deleted Items folder
• Junk Email folder retention period

A soft-deleted user mailbox is recoverable within 30 days of deletion.

Retention limits

¹ Default for Microsoft 365 is 14 days for items removed from Deleted Items (admin can change to max 30 days).

Retention limits across standalone options

¹ Default limit for Exchange Server can be changed.
² Default for Exchange Online is 14 days (admin can change to max 30 days).

Call to Action (CTA)

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