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M365 Outlook (Information) 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.
Mailbox folder limits
- 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 in 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 Microsoft 365 options
| Feature | Microsoft 365 Business Essentials | Microsoft 365 Business Premium | Microsoft 365 Enterprise E1 | Microsoft 365 Enterprise E3 | Microsoft 365 Enterprise E5 | Microsoft 365 Enterprise F1 |
| Maximum number of messages per mailbox folder | 1 million | 1 million | 1 million | 1 million | 1 million | 1 million |
| Warning for number of messages per mailbox folder | 900,000 | 900,000 | 900,000 | 900,000 | 900,000 | 900,000 |
| Maximum number of messages per folder in the Recoverable Items folder | 3 million | 3 million | 3 million | 3 million | 3 million | 3 million |
| Storage quota for Recoverable Items folder in primary mailbox (not on hold) | 30 GB | 30 GB | 30 GB | 30 GB | 30 GB | 30 GB |
| Storage quota for Recoverable Items folder in primary mailbox (on hold) | 100 GB | 100 GB | 100 GB | 100 GB | 100 GB | 100 GB |
| Storage quota for Recoverable Items folder in archive mailbox (not on hold) | 30 GB | 30 GB | 30 GB | Unlimited2 | Unlimited2 | 30 GB |
| Storage quota for Recoverable Items folder in archive mailbox (on hold) | 100 GB1 | 100 GB1 | 100 GB1 | Unlimited2 | Unlimited2 | 100 GB1 |
| Warning for number of messages per folder in the Recoverable Items folder | 2.75 million | 2.75 million | 2.75 million | 2.75 million | 2.75 million | 2.75 million |
| Maximum number of subfolders per mailbox folder | 10,000 | 10,000 | 10,000 | 10,000 | 10,000 | 10,000 |
| Warning for number of subfolders per mailbox folder | 9000 | 9000 | 9000 | 9000 | 9000 | 9000 |
| Maximum folder hierarchy depth | 300 | 300 | 300 | 300 | 300 | 300 |
| Warning for folder hierarchy depth | 250 | 250 | 250 | 250 | 250 | 250 |
| Maximum number of public folders | 500,000 | 500,000 | 500,000 | 500,000 | 500,000 | Not available |
| Maximum number of subfolders per public folder | 10,000 | 10,000 | 10,000 | 10,000 | 10,000 | Not available |
| Warning for number of subfolders per public folder | 9000 | 9000 | 9000 | 9000 | 9000 | Not available |
Notes:
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 unlimited 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 unlimited archiving in Microsoft 365. See the Microsoft 365 Roadmap for details about availability of auto-expanding archiving.
Mailbox folder limits across standalone plans
| Feature | Exchange Server 2013 | Exchange Online Plan 1 | Exchange Online Plan 2 | Exchange Online Kiosk |
| Maximum number of messages per mailbox folder | No limit1 | 1 million | 1 million | 1 million |
| Warning for number of messages per mailbox folder | No limit | 900,000 | 900,000 | 900,000 |
| Maximum number of messages per folder in the Recoverable Items folder | No limit | 3 million | 3 million | 3 million |
| Storage quota for Recoverable Items folder in primary mailbox (not on hold) | 30 GB | 30 GB | 30 GB | 30 GB |
| Storage quota for Recoverable Items folder in primary mailbox (on hold) | 100 GB | 100 GB | 100 GB | 100 GB |
| Storage quota for Recoverable Items folder in archive mailbox (not on hold) | 30 GB | 30 GB | 30 GB | 30 GB |
| Storage quota for Recoverable Items folder in archive mailbox (on hold) | 100 GB2 | 100 GB2 | Unlimited3 | Unlimited3 |
| Warning for number of messages per folder in the Recoverable Items folder | No limit | 2.75 million | 2.75 million | 2.75 million |
| Maximum number of subfolders per mailbox folder | No limit | 1000 | 1000 | 1000 |
| Warning for number of subfolders per mailbox folder | No limit | 900 | 900 | 900 |
| Maximum folder hierarchy depth | No limit | 300 | 300 | 300 |
| Warning for folder hierarchy depth | No limit | 250 | 250 | 250 |
| Maximum number of public folders | 1,000,000 | 100,000 | 100,000 | Not available |
| Maximum number of subfolders per public folder | N/A | 1,000 | 1,000 | Not available |
| Warning for number of subfolders per public folder | N/A | 900 | 900 | Not available |
Notes:
1 Microsoft recommends no more than 1,000,000 messages per mailbox folder.
2 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 unlimited 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.
3 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 . See the Microsoft 365 Roadmap for details about availability of auto-expanding archiving.
Message limits
The following limits are applied to every email message.
- 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 Microsoft 365 now supports larger email messages.
Note: Particular email users 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.
- Message header size limit Specifies the maximum size of all message header fields in a message.
- The current limit is 256 KB.
- If the total size of all message headers exceeds 256 KB, Exchange Online will reject the message with error "552 5.3.4 Header size exceeds fixed maximum size."
- The size of the message body or attachments isn't considered.
- Because the header fields are plain text, the size of the header is determined by the number of characters in each header field and by the total number of header fields.
- Each text character consumes 1 byte.
- 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.
- Note: This is the maximum file size of a single attachment. Individual user 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
| Feature | Microsoft 365 Business Essentials | Microsoft 365 Business Premium | Microsoft 365 Enterprise E1 | Microsoft 365 Enterprise E3 | Microsoft 365 Enterprise E5 | Microsoft 365 Enterprise F1 |
| Message size limit - Outlook | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 |
| Message size limit - OWA | 112 MB1,3 | 112 MB1,3 | 112 MB1,3 | 112 MB1,3 | 112 MB1,3 | 112 MB1,3 |
| Message size limit - Outlook for Mac | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 | 150 MB1,2 |
| Message size limit - migration | 150 MB4 | 150 MB4 | 150 MB4 | 150 MB4 | 150 MB4 | 150 MB4 |
| Size limit for encrypted messages (for subscribers using Office 365 Message Encryption with new capabilities)5 | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB |
| Size limit for encrypted messages (for subscribers using Office 365 Message Encryption legacy version)5 | 25 MB | 25 MB | 25 MB | 25 MB | 25 MB | 25 MB |
| Subject length limit | 255 characters | 255 characters | 255 characters | 255 characters | 255 characters | 255 characters |
| File attachments limit | 250 attachments | 250 attachments | 250 attachments | 250 attachments | 250 attachments | 250 attachments |
| File attachment size limit - Outlook | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB |
| File attachment size limit - OWA 6 | 35 MB | 35 MB | 35 MB | 35 MB | 35 MB | 35 MB |
| File attachment size limit - Outlook for Mac | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB | 150 MB |
| Multipart message limit | 250 parts | 250 parts | 250 parts | 250 parts | 250 parts | 250 parts |
| Embedded message depth limit | 30 embedded messages | 30 embedded messages | 30 embedded messages | 30 embedded messages | 30 embedded messages | 30 embedded messages |
Notes:
1 The default maximum message size for Office 365 mailboxes is 25 MB. Office 365 Administrators can specify a custom limit between 1 MB and 150 MB. However, the size of message you can send or receive also depends on what your email user or solution supports. For more information about customizing the maximum allowed message size for your organization, see Microsoft 365 now supports larger email messages.
2 You can send and receive up to 150 MB messages between Microsoft 365 users (where the message never leaves the Microsoft 365 datacenters). Messages that are routed outside of the Microsoft 365 datacenters are subject to an additional 33% translation encoding increase, in which case the maximum message size is 112 MB
3 OWA accounts for the possibility that your message may be subject to the 33% encoding increase and restricts the size of message you can send to 25% less than the configured setting. For example, if you customize your settings for a 100 MB maximum message size, you can send messages no larger than 75 MB.
4 The size of messages to be moved into Exchange Online are computed by Exchange Online. Versions of Exchange prior to Exchange Server 2013 may report a smaller item size. This limit applies to move based migrations using any supported Exchange Mailbox Replication Service. Other migration methods (Cutover, Staged, IMAP, PST) and other third party tools are limited by the general message size limit.
5 For information about OME with new capabilities, see Set up new Microsoft 365 Message Encryption capabilities built on top of Azure Information Protection
6 You cannot attach a single file that exceeds 35 MB. Additionally, you cannot attach files that collectively exceed 35MB. For example, if you attach one 34MB file, you can only attach an additional 1 MB file.
Message limits across standalone options
| Feature | Exchange Server 2013 | Exchange Online Plan 1 | Exchange Online Plan 2 | Exchange Online Kiosk |
| Message size limit - Outlook | 10 MB4 | 150 MB1,2 | 150 MB1,2 | 150 MB2 |
| Message size limit - OWA | 10 MB4 | 112 MB1,3 | 112 MB1,3 | 150 MB1,2 |
| Message size limit - Outlook for Mac | 10 MB4 | 150 MB | 150 MB | |
| Message size limit - migration | Not applicable | 150 MB5 | 150 MB5 | 150 MB5 |
| Size limit for encrypted messages (for subscribers using Office 365 Message Encryption with new capabilities)6 | 150 MB | 150 MB | 150 MB | 150 MB |
| Size limit for encrypted messages (for subscribers using Office 365 Message Encryption legacy version)6 | 25 MB | 25 MB | 25 MB | 25 MB |
| Subject length limit | 255 characters | 255 characters | 255 characters | 255 characters |
| File attachments limit | 1024 attachments4 | 250 attachments | 250 attachments | 250 attachments |
| File attachment size limit - Outlook | 35 MB4 | 150 MB | 150 MB | 150 MB |
| File attachment size limit - OWA | 35 MB4 | 35 MB | 35 MB | 35 MB |
| File attachment size limit - Outlook for Mac | 35 MB4 | 150 MB | 150 MB | 35 MB |
| Multipart message limit | 250 parts | 250 parts | 250 parts | 250 parts |
| Embedded message depth limit | 30 embedded messages | 30 embedded messages | 30 embedded messages | 30 embedded messages |
Notes:
1 Microsoft 365 Administrators can specify a custom limit between 1 MB and 150 MB. However, the size of message you can send or receive also depends on what your email user or solution supports. For more information about customizing the maximum allowed message size for your organization, see Microsoft 365 now supports larger email messages.
2 You can send and receive up to 150 MB messages between Microsoft 365 users (where the message never leaves the Microsoft 365 datacenters). Messages that are routed outside of the Microsoft 365 datacenters are subject to an additional 33% translation encoding increase, in which case the maximum message size is 112 MB.
3 OWA accounts for the possibility that your message may be subject to the 33% encoding increase and restricts the size of message you can send to 25% less than the configured setting. For example, if you customize your settings for a 100 MB maximum message size, you can send messages no larger than 75 MB.
4 This is the default limit for Exchange Server 2013 organizations. Administrators can change this value for their organization.
5 The size of messages to be moved into Exchange Online are computed by Exchange Online. Versions of Exchange prior to Exchange Server 2013 may report a smaller item size.
6 For information about OME with new capabilities, see Set up new Microsoft 365 Message Encryption capabilities built on top of Azure Information Protection.
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.
| Feature | M365 Business Essentials | M365 Business Premium Office | M365 Enterprise E1 | M365 Enterprise E3 | M365 Enterprise E5 | M365 Enterprise F1 |
| Messages received | 3,600 messages per hour | 3,600 messages per hour | 3,600 messages per hour | 3,600 messages per hour | 3600 messages per hour | 3600 messages per hour |
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.
Note: For distribution groups stored in an organization's 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.
- 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.
Note: 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.
Note: 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 over consumption of system resources by a single sender. If a user submits messages at a rate that exceeds the limit via SMTP user submission, the messages will be rejected and the user will need to retry.
Sending limits across Microsoft 365 options
| Feature | Microsoft 365 Business Essentials | Microsoft 365 Business Premium | Microsoft 365 Enterprise E1 | Microsoft 365 Enterprise E3 | Microsoft 365 Enterprise E5 | Microsoft 365 Enterprise F1 |
| Recipient rate limit | 10,000 recipients per day | 10,000 recipients per day | 10,000 recipients per day | 10,000 recipients per day | 10,000 recipients per day | 10,000 recipients per day |
| Recipient limit | 500 recipients | 500 recipients | 500 recipients | 500 recipients | 500 recipients | 500 recipients |
| Recipient proxy address limit | 400 | 400 | 400 | 400 | 400 | 400 |
| Message rate limit | 30 messages per minute | 30 messages per minute | 30 messages per minute | 30 messages per minute | 30 messages per minute | 30 messages per minute |
Sending limits across standalone options
| Feature | Exchange Server 2013 | Exchange Online Plan 1 | Exchange Online Plan 2 | Exchange Online Kiosk |
| Recipient rate limit | No limit1 | 10,000 recipients per day | 10,000 recipients per day | 10,000 recipients per day |
| Recipient limit | 500 recipients1 | 500 recipients | 500 recipients | 500 recipients |
| Recipient proxy address limit | 400 | 400 | 400 | 400 |
Note:
1 This is the default limit for Exchange Server 2013 organizations. Administrators can change this value for their organization.