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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.
- The 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 the 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.
- The 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 the 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.
- The 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 the 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.
- The 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 Office 365
| Feature | Exchange Server 2013 | Office 365 Small Business | Office 365 Small Business Premium | Office 365 Midsize Business | Office 365 Enterprise E1Office 365 Education A2Office 365 Government G1 | Office 365 Enterprise E3Office 365 Education A3Office 365 Government G3 | Office 365 Enterprise E4Office 365 Education A4Office 365 Government G4 | Office 365 Enterprise K1Office 365 Government K1 |
|---|---|---|---|---|---|---|---|---|
| Maximum number of messages per mailbox folder | No limit | 1 million | 1 million | 1 million | 1 million | 1 million | 1 million | 1 million |
| Warning for number of messages per mailbox folder | No limit | 900,000 | 900,000 | 900,000 | 900,000 | 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 | 3 million | 3 million | 3 million | 3 million |
| Warning for number of messages per folder in the Recoverable Items folder | No limit | 2.75 million | 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 | No limit | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 |
| Warning for number of subfolders per mailbox folder | No limit | 900 | 900 | 900 | 900 | 900 | 900 | 900 |
| Maximum folder hierarchy depth | No limit | 300 | 300 | 300 | 300 | 300 | 300 | 300 |
| Warning for folder hierarchy depth | No limit | 250 | 250 | 250 | 250 | 250 | 250 | 250 |
| Maximum number of public folders | 10,000 | 100,000 | 100,000 | 100,000 | 100,000 | 100,000 | 100,000 | N/A |
| Maximum number of subfolders per public folder | N/A | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | N/A |
| Warning for number of subfolders per public folder | N/A | 900 | 900 | 900 | 900 | 900 | 900 | N/A |
Mailbox folder limits across Microsoft Office 365 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 limit | 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 |
| 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 | 1,000 | 1,000 | 1,000 |
| 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 | 10,000 | 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 | N/A |