M365 Outlook (Information) Exchange Online Limits

This article details microsoft 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 fit into one of the following categories:

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 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.


Keywords:
Exchange, limits, Microsoft, 
Doc ID:
90064
Owned by:
Help Desk K. in UW-Milwaukee Help Desk
Created:
2019-02-28
Updated:
2023-07-13
Sites:
UW-Milwaukee Help Desk