What are throttling policies in Exchange Online?

Question

Can you explain in detail what throttling policies are in Exchange Online, including their purpose, how they function, and the impact they have on performance and resource management? Additionally, please discuss any specific scenarios where throttling policies might be adjusted and the best practices for managing these policies to ensure optimal system performance and user experience.

Accepted Answer

Throttling policies in Exchange Online are a set of rules designed to manage system resources efficiently and ensure optimal performance and reliability. They help in regulating the amount of server resources a user or an application can consume. By doing so, throttling policies prevent any single user or application from monopolizing resources, which could degrade the performance for other users.

### Purpose:
1. **Resource Management:** Throttling policies are employed to maintain a balance in resource usage among all users and services within Exchange Online.
2. **System Performance:** By limiting excessive resource consumption, throttling ensures that system performance remains stable, even during peak times.
3. **Fair Usage:** They ensure fair usage by preventing resource exhaustion that could be caused by a single user or application, thus contributing to overall system reliability.

### Functionality:
Throttling policies work by limiting the number of concurrent connections, the frequency of calls, and the amount of data that can be processed within a given time frame. These limits can be applied to various operations, such as:
- **PowerShell Commands:** Limits the number of simultaneous PowerShell sessions that can be opened.
- **Email Operations:** Controls the number of messages users can send, receive, or the frequency of message-related operations.
- **API Requests:** Restricts the rate and volume of API requests that applications can make.

### Impact on Performance and Resource Management:
- **Improved Stability:** By ensuring that no user or application consumes excessive resources, overall system stability is enhanced.
- **Predictable Performance:** Throttling policies allow for more predictable performance, which is crucial for maintaining service level agreements (SLAs).
- **Balanced Load:** By spreading resource use more evenly, throttling helps prevent server overloads and reduces the risk of outages.

### Scenarios for Adjusting Throttling Policies:
1. **Migration Projects:** During email migrations, throttling settings might need adjustment to allow for increased data transfer without hitting rate limits.
2. **High-Volume Periods:** Organizations might adjust policies temporarily during anticipated periods of heavy use.
3. **Application Needs:** Custom applications with legitimate high resource demands might require tailored policies to function efficiently without being throttled.

### Best Practices for Managing Throttling Policies:
- **Monitor and Analyze Usage:** Continuously monitor resource usage to identify trends or patterns that might require policy adjustments.
- **Custom Policies:** Where necessary, create and assign custom throttling policies for users or applications with specific demands.
- **Communicate Changes:** Inform affected users and administrators about any changes to throttling policies to prepare them for adjustments in system behavior.
- **Use Default Policies Wisely:** Often, the default settings are sufficient for most users, so changes should be made judiciously to maintain system integrity.

Overall, throttling policies in Exchange Online are essential for maintaining an equitable and efficient environment. Properly managing these policies—by adjusting them only when necessary and following best practices—can ensure that users enjoy a seamless and uninterrupted experience.

What are throttling policies in Exchange Online?

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