I am aware that there are various protocols by which MS Exchange exposes access to services - including:

  • EAS : Exchange Active Sync - A proprietary protocol that appears to be the default option for access to Exchange from mobile devices.
  • EWS : Exchange Web Services - An openly documented SOAP protocol- a standard Web Service with a WSDL definition.
  • Exchange Outlook Anywhere (also known as RPC/HTTP) ...now deprecated in favour of MAPI over HTTP?

If I only have access to Exchange Web Services, for a particular Exchange Server, is there any way to access those services using Outlook Mobile (on Android, iOS or Win-10-phone)?

If direct access is not viable, is there such a thing as an Exchange-Active-Sync (client-side) to Exchange-Web-Services (server-side) bridge?

If no bridge between EAS and EWS exists, is it feasible to deploy Outlook Web App to present EWS services in web browsers on phones? (Essentially, can Outlook Web App be configured to, exclusively, communicate with Exchange using EWS via a Web Proxy?)

If none of the above are feasible, can I use Outlook (on a Windows laptop) to connect to the EWS Service?


1# General mobile devices use ActiveSync to connect to Exchange server.

2# No such bridge between different services.

3# Different protocols are for different services. For example, EWS service is mainly responsible for free/busy, OOF, mailtips and Outlook for Mac connection. ActiveSync is for mobile devices to access. RPC/HTTP and MAPI/HTTP are for Outlook connection. But it doesn't mean that only one protocol is needed for a specific client. For example, even when the Outlook connects to Exchange via RPC/HTTP, it will connect to EWS service when querying free/busy data.

Actually, all of the protocols you mentioned above are based on HTTPS, they use the same port TCP 443 and same certificate(binding with IIS service on Exchange server). And we always use the same namespace for Outlook Anywhere, ActiveSync, EWS service, OAB virtual directory and MAPI/HTTP, such as mail.domain.com.

For the internal clients, there would be no need to limit these services.

For the external clients, make sure to publish the namespace autodiscover.domain.com, mail.domain.com, and the MX records. If you have firewall or proxy server, you may need to set the rule to publish these services. You can google the document related to the firewall/proxy setting you plan to use.

Here is a blog about client access in Exchange 2013, for your reference: https://blogs.technet.microsoft.com/exchange/2013/01/25/exchange-2013-client-access-server-role/

Hope the above information helps.:)

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  • Thanks, it helps. I am considering these questions from the perspective of establishing if access to specific mailboxes, calendars - etc. can be audited at an HTTP proxy. This drew me to the open, documented, EWS SOAP protocol. I had hoped that, as EWS supports Outlook on Mac, that it it provides all the features required to implement the proprietary ActiveSync protocol. I assume, from your answer, that it is not feasible to route Outlook Mobile requests over EWS for any server-side configuration? – aSteve Jun 14 '17 at 6:10
  • No, Steve. As far as I know, it's not feasible to route Outlook Mobile requests over EWS, because they are different services and designed for different purpose. – Sue.J Jun 14 '17 at 8:24
  • FWIW, Microsoft's protocol designs do not preclude "Outlook-like" functionality on mobile. MailDroid demonstrate that EWS can be used on mobile for e-mail. AquaMail shows the same with e-mail+Calendar. I suppose it's just that Microsoft didn't see a reason to implement e-mail/calendar connectivity via EWS in their Android Outlook app. – Robert Fleming May 17 '19 at 21:50

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