When planning and designing Microsoft 365 based solutions, including Exchange Online, Exchange Online Protection, Sharepoint Online, Teams, Yammer, Compliance, Security and various other supplementary Microsoft 365 services, such as Sway, it is critical to always take into consideration the resource limits of each Microsoft 365 service. Microsoft 365 service resource limits are enforced using quotas (limits) and throttling. Azure Active Directory (Azure AD) and the individual Microsoft 365 services use both quotas and throttling. Limits are service-specific and change over time as new capabilities are added. You should consult the following articles for more details on each service:
- Azure AD service limits and restrictions
- Exchange Online Limits
- SharePoint Online software boundaries and limits
- Sharepoint Online and Onedrive for Business restrictions
- Sharepoint Online top five limitations
- Skype for Business Limits
- Teams limits
- Yammer REST API and Rate Limits
- File Size Limits in Sway
The limits in Microsoft Exchange Online fit 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
In addition to the above limits, there are further throttling mechanisms which are used throughout Azure AD and Microsoft 365. Throttling within the service is especially important, given that network resources in Microsoft’s datacenters are optimized for the broad set of customers that use the services. Throttling mechanisms include the following:
- Azure AD and Microsoft 365 feature user-level throttling, which limit the number of transactions or concurrent calls (by script or code) that can be performed by a single user.
- A default PowerShell throttling policy is assigned to each tenant at tenant creation. These settings affect other items, such as the maximum number of simultaneous PowerShell sessions that can be opened by a single administrator.
- Each Exchange Online customer has a default Exchange Web Services (EWS) policy that is tuned for EWS client operations, and throttling that applies to all Outlook clients.
It is recommended to also run a Web search on “[Microsoft 365 service] limits“, where [Microsoft 365 service] is the name of the service you are designing.