Which Exchange protocol to use?

Question

My company is working on a project to develop a desktop and mobile email client that can connect to different mail servers with minimal configuration for users or server admins. We want to be able to support Exchange but I've realised after some research that there are a number of issues to think about. Our goal is to be able to connect to as many types of Exchange server as possible, so we need to choose a protocol, or protocols to implement that will allow that. It seems there are 3 different protocols in use - WebDAV for older 2000/2003/2007 servers, Exchange Web Services (EWS) for 2007/2010+ servers and ActiveSync which is supported by everything post 2003 (I think).

My question is, which do you think is the best approach for implementation?

-ActiveSync seems to have the most coverage but is the biggest pain to implement. Would a dual implementation of WebDAV + EWS provide the same coverage?

Also, if there are any Exchange Admins out there, which protocols tend to be enabled by default? If WebDAV/EWS are always turned off by default then maybe ActiveSync is the only option. It seems that as the iPhone and Android support ActiveSync it is most likely to be turned on, but what about the others?

Also, would be interesting to have statistics of what servers are currently in use - i.e. how many are still using 2003, have migrated to 2010 etc.

Would like to hear your opinions.

Cheers, Kevin

Answer 1

If you are building an email client and targeting Exchange, I would recommend ActiveSync. The other protocols -- WebDAV and EWS -- were not intended for generic email clients. EWS, for example, does not support transactions or syncing, so if you have multiple clients you will have to deal with tons of race conditions on your own. WebDAV requires some funky limitations and is not always enabled. ActiveSync is relatively easy to write, it just requires getting a license from Microsoft, and it always works with Exchange.

If you just want to send and read email, however, don't overlook IMAP and POP3. You'll find the broadest support for those, even though are disabled in the newest installations.