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Choosing between Exchange ActiveSync and EWS

Exchange Server 2010

Explore the differences between the Exchange ActiveSync and EWS protocols for Exchange client application development.

Applies to:  Exchange 2013 | EWS Managed API 

In this article, we’ll examine how the Exchange ActiveSync and Exchange Web Services (EWS) protocols integrate with Exchange. Although the two protocols provide similar functionality, they are designed to target different scenarios and different types of applications.

The Exchange ActiveSync protocol is designed for direct mobile device sync with Exchange, including lightweight clients, such as the Windows 8 Mail and Calendar application, that can be used in mobile scenarios. Exchange ActiveSync is optimized for low-bandwidth applications, such as messaging applications that run on mobile devices. Enhancements to the Exchange ActiveSync protocol primarily support stability and reliability for mobile device scenarios.

The EWS protocol provides rich functionality that enables you to add features similar to those in Outlook to your desktop applications. EWS enables efficient and well-managed server-to-server communications. Investments in EWS functionality continue to enable rich and comprehensive interactions with Exchange.

Office 365 customers expect that access to sensitive information stored in data centers is protected and that the service performance is reliable. In order to better deliver consistent, secure, and high-quality services, we define and adhere to standard operating procedures and structured interaction methods for Office 365. One part of this strategy is to use the product — in this case Exchange and Exchange Online — in the way it was designed to work.

Exchange ActiveSync is not designed to be used for server-to-server communications in the online environment, and we do not license Exchange ActiveSync for this purpose. Within the Office 365 environment, Exchange ActiveSync connections from applications and servers or services other than from mobile clients or client applications serving an individual user might be throttled or refused. We cannot guarantee that applications and servers or services that currently work with Office 365 will continue to work in the same way, or at all, over time.

Exchange on-premises deployments include functionality that enables administrators to enforce controls similar to what we enforce on Office 365. Nevertheless, many customers share the same security and performance concerns that drive decisions in the Office 365 environment. Because Exchange ActiveSync uses protective measures to prevent service degradation, such as automatic throttling, using Exchange ActiveSync for server-to-server communications in this environment might result in a poor user experience. For this and other reasons, we do not recommend that you use Exchange ActiveSync for scenarios other than those for which it was designed.

Using Exchange ActiveSync for server-to-server communications in hybrid deployments (deployments that include on-premises and Office 365 mailboxes) is also not recommended for these reasons.

Exchange ActiveSync works well for mobile device sync of email, calendar, contacts, tasks, and notes. You can also use Exchange ActiveSync for some client integration with Exchange; however, it is not designed to be used for server-to-server communications. The protocol is optimal for efficient sync communication between a mobile device and an Exchange server or service, and is often the preferred protocol for Personal Information Manager (PIM) sync applications on mobile devices. Consider the following when deciding whether to use Exchange ActiveSync for your client application:

  • When you use Exchange ActiveSync for mobile device sync, you must accurately report device capabilities so that the device will be compatible with Exchange mobile device policies. You should also represent the connected device by using approved device type and device name labels. This will enable Exchange administrators to use the built in Allow/Block/Quarantine functionality to control Exchange ActiveSync access. If you are using Exchange ActiveSync for other scenarios, be aware that Exchange administrators can block Exchange ActiveSync traffic from sources that they have not explicitly approved. For this reason, we launched the Exchange ActiveSync logo program to identify mobile devices that meet Exchange ActiveSync certification requirements. Exchange administrators can then easily recognize devices and will not inadvertently block traffic to and from these devices.

  • Exchange ActiveSync can be used for mail client communications, but it can access only a limited number of mailbox item properties. Items that fall outside the defined set, including custom messages from line-of-business applications or InfoPath forms, cannot be synced by using Exchange ActiveSync.

  • Search in Exchange ActiveSync is limited to a single string and a maximum of 200 results.

  • Exchange ActiveSync doesn’t support the Drafts folder.

  • Microsoft Premier Support for Developers offers services to assist in the design and implementation of Exchange ActiveSync clients on mobile devices that sync directly with Exchange.

EWS provides feature-rich access to mail, calendar, contacts, tasks, notes, and directory services, as well as other services such as the Availability web service (for free/busy information) and smart meeting booking. EWS enables rich scenarios that leverage the unique business logic in Exchange,  and is the preferred protocol for developing powerful and flexible desktop and server applications. The following are some considerations for using EWS for Exchange client development:

  • EWS exposes many properties that are not available through Exchange ActiveSync that enable you to achieve a rich Outlook experience. For example, only EWS exposes the following properties on tasks: Actual Work, Assigned Time, Billing Information, Companies, IsTeamTask, Mileage, and Owner, as well as Task delegation fields.

  • EWS has extended property support that allows arbitrary MAPI properties to be set or retrieved, enabling the client to make use of features not exposed in the protocol. For example, neither EWS nor Exchange ActiveSync natively support the ability to set the Description field on a folder or the Billing Information field on a calendar item, both of which Outlook can display. However, it is possible to retrieve both properties by using the underlying MAPI property addressing mechanism in EWS. EWS provides access to all mail item classes.

  • EWS provides a way to add and remove delegates (those who can send email or manage a calendar on your behalf). EWS also enables access mailbox, folders, and calendars that others have shared with you.

  • EWS enhances meeting scheduling by providing an API that returns free/busy information for users with whom you are scheduling meetings, and provides smart meeting time suggestions (based on when users and rooms are available).

  • EWS provides rich search capabilities and allows you to search on many mail message fields and custom fields, including recipients, subject, body, sent/received date, and importance.

  • EWS allows you to expand distribution lists or groups so users can see the members of a distribution list when they are browsing the directory or composing an email message to a distribution list.

  • EWS provides access to public folders.

  • EWS supports creating and saving email messages in a Drafts folder.

  • EWS enables you to create and access search folders; for example, all unread email, all flagged items, and all items with a particular category. Some search folders are created by default in Outlook and Exchange. They provide a great way to create different views and triage email messages.

  • EWS allows access to and creation of personal distribution lists. Personal distribution lists are user-defined groups stored in the user's Contacts folder.

  • EWS provides access to user configuration information, including time zones, working hours, and all end-user settings for Outlook Web App and Exchange ActiveSync.

  • EWS supports impersonation and on-behalf-of functionality.

  • EWS does not support setting and requiring mobile device policies. You cannot execute the remote wipe of a mobile device by using EWS.

  • Microsoft Premier Support for Developers offers services to assist in the design and implementation of EWS applications that interact with Exchange.

There’s a perception that Exchange ActiveSync is more broadly deployed than EWS. Although it's true that robust Exchange ActiveSync support was initially included in Exchange Server 2003, and EWS support started in Exchange Server 2007, it is also true that the Exchange 2003 installed base continues to decline as customers move to more current versions of Exchange.

Most organizations running versions of Exchange starting with Exchange 2007 expose EWS and Exchange ActiveSync equally. Some applications that use EWS for Exchange connectivity include the Mail, Calendar, and Contacts apps native in Apple Mac OS X, BlackBerry’s Business Cloud Services and BlackBerry Enterprise Server for Office 365, versions of Office starting with Office 2007 (including significant Outlook Anywhere functionality), and Office for Mac.

You might need a patent license to use Exchange ActiveSync. We have created licensing programs for scenarios in which the intended use of the protocol aligns with the design focus and anticipated uses of the protocol.

For more information about our licensing programs, see the Intellectual Property Licensing Group.

We’ve outlined some of the technical differences between Exchange ActiveSync and EWS, as well as some business considerations to help you make an informed decision as to which protocol is best for your application and your customer experience.

For more information about Exchange development, see the Exchange Server Developer center. For more information about EWS development, see Web services in Exchange 2013.

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