About: Exchange Server ActiveSync (EAS)

API Type:  Mailbox Assessor
API Interface: APIs which can send a POST.
Business Logic: Works with  mailbox and public folder content including items, folders and special settings.
Development Languages: N/A.
Property Access: Yes
Product Versions:
Exchange 2003, 2007, 2010, 2013, Exchange Online.


Exchange Server ActiveSync (EAS) is a very light fixed schema API which uses WBXML (tokenized XML) which allows a device (such as a phone or tablet) to communicate with Exchange.  Developer support for client-side development is only provided to customers who have a Premier support agreement and have licensed EAS for client side development.  There is no developer support for server side development, however there are server side licensing options.  It is extremely important that if you are considering to commercialize an application which uses EAS that you obtain licensing from Microsoft as licensing is heavily enforced for EAS.

EAS is meant for devices such as cell phones or tablets to sync with Exchange.  Its functionality is very targeted and because of that it has only the needed functionality to sync basic mailbox data such as email, contacts and calendar content.  If you want something more full-blown then look at an API such as Exchange Web Services (EWS).

Some Points Of Interest:

  • EAS cannot access custom/MAPI properties. The schema is fixed.
  • EAS cannot be used to perform administrative tasks – such as turning on logging or mailbox maintenance.
  • The EAS schema has only changed during an RTM or full Exchange release in the past.
  • Its up to each EAS device to honor Exchange provisioning settings.
  • There are no Microsoft APIs which do EAS calls – such as the Exchange EWS Managed API which is a .NET wrapper for EWS calls.
  • There are some third party APIs which do wrap EAS calls – however, those are not supported by Microsoft.
  • If you use a third party API for EAS then understand that you still need to license.
  • EAS is not supported with delegate access. Delegate access is what is used for shared mailbox access.  It also does not support impersonated access.  EAS should only meant for a user to access their own email, calendar, contacts, etc. This is true for all versions of EAS between 2.5 and 14.1.


New to Exchange ActiveSync Development?
This is a blog which I wrote a while back and which I try to keep up to date on EAS development.

Exchange Server Protocols Technical Documents
Note:  EAS documentation starts with “MS-AS”

Microsoft Exchange Server Interoperability Guidance

Exchange ActiveSync

Also see:

About: Mailbox Accessing APIs

About: Messaging APIs

Exchange and Outlook Development Help




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