Microsoft Exchange, the ubiquitous email and calendaring platform, serves as the communication backbone for countless organizations. For developers and product teams seeking to integrate with this data and functionality, navigating the complex landscape of Microsoft Exchange APIs can be daunting.

This blog post cuts through the clutter, highlighting the key Exchange APIs you need to know about in 2024:

  1. Microsoft Graph API: This RESTful API provides programmatic access to a vast range of Outlook data and functionalities, offering flexibility and control for developers.

    Think of Graph API as the Swiss Army Knife of Microsoft services. It encompasses access to Exchange data alongside other Microsoft offerings like SharePoint, OneDrive, and Azure AD.

    It is the recommended way for accessing Exchange Online (Office 365 and but not for Exchange Server on-premises! Check out this post: The End of the REST API for On-Premises Mailboxes Preview.

  2. Outlook API: Before the introduction of the Microsoft Graph API, Microsoft provided a separate RESTful API specifically for Outlook, known as the Outlook REST API. This API offered programmatic access to Outlook data and functionalities but was eventually decommissioned in favor of the Graph API.

  3. Exchange Web Services (EWS): This SOAP-based legacy web service allows developers to access and manipulate Outlook data using XML messages. It is the recommended way for accessing Exchange Server on-premises! Don’t use EWS for accessing Exchange Online: Retirement of Exchange Web Services in Exchange Online.

  4. Messaging Application Programming Interface (MAPI): This was the original API for Outlook that offered deep access and control over Outlook data. It’s not actively developed anymore. Microsoft is pushing developers towards the newer and more versatile Microsoft Graph API for integrating with Outlook and other Microsoft services.

  5. ActiveSync: This legacy protocol enables seamless synchronization of Outlook data with mobile devices, ensuring users have access to their information on the go. It’s no longer actively developed, and its future remains uncertain. The rise of newer technologies and Microsoft’s focus on modern APIs point towards a potential phase-out in the future.

Choosing the Right Exchange API

Now that we’ve explored the key Microsoft Exchange APIs, the crucial question remains: Which one is right for your project?

Factors to Consider:

Deployment Environment:

  • Exchange Online (Office 365 and Microsoft Graph API reigns supreme. EWS is retired, and Outlook REST API is deprecated.
  • Exchange Server on-premises: EWS is the go-to choice, while MAPI remains an option for specific needs (but consider future-proofing).
  • Functionality Requirements:

Basic data access and management:

  • Graph API or Outlook REST API (for online) and EWS (for on-premises) suffice.
  • Advanced features and deep control: EWS or MAPI (for on-premises only) offer more depth.
  • Mobile device synchronization: ActiveSync is still functional, but consider modern alternatives like Microsoft Intune (cloud-based unified endpoint management).

Development Resources:

  • RESTful APIs (Graph and Outlook REST): More developer-friendly with readily available tools and libraries.
  • SOAP-based EWS: Requires XML expertise and specific libraries.
  • MAPI: C++-based, demanding deeper technical knowledge.


  • Microsoft Graph API: Actively developed and supported, ensuring longevity.
  • Other APIs: EWS is retired for online, Outlook REST API is deprecated, MAPI lacks active development, and ActiveSync’s future is uncertain.

Decision Tree:

Here’s a simplified decision tree to guide your API selection:

|  Is your deployment environment:                   |
|                                                    |
|  +--------+  +-----------------+                   |
|  | Online |  | On-premises     |                   |
|  +--------+  +-----------------+                   |
|                                                    |
|  +-----------------------------------------------+ |
|  | Do you need deep control and legacy features? | |
|  |                                               | |
|  | +-----+  +----+                               | |
|  | | Yes |  | No |                               | |
|  | +-----+  +----+                               | |
|                                                  | |
|  +---------+  +-----------+                      | |
|  | Use EWS |  | Use Graph |                      | |
|  | or MAPI |  | API       |                      | |
|  +---------+  +-----------+                      | |