Outlook Web Access – A catalyst for web evolution


“The Exchange Web Client” was the first web email client produced by Microsoft.  It had an interesting green and black color scheme but it did most of the basic needs for doing messaging.  We didn’t have enough time to add calendaring support in the first version.  What we did in this first version was the first step in what has now become a new way of building web applications.


OWA was born out of the sheer will of my friend Bob Gering when he decided we should look exactly like Outlook.  We started changing our frameset design, colors and graphics to look and feel like Outlook.  It was this desire to look, act and feel like Outlook that caused us to move web applications forward in a new evolutionary path.


Traditional web applications constantly refresh the document for just about every action. During Exchange 5.5 development in 1996/97 we used hidden frames to communicate to the server when sending messages so we wouldn’t clear the user’s document.  However, we still had many frames updating during navigation of the mailbox.  We also developed a Java applet for the date picker control in the calendar view to augment the user experience since DHTML on the current browsers at that time was just about non-existent.  In the end we found that the applet did not meet our performance needs because virtual machine initialization was too expensive. OWA 5.5 had richer support than prior versions but it still lacked the type of experience that users get in a win32 application but it did work on just about every browser under the sun.


In 1998 we started on the incredible task of rewriting OWA for Exchange 2000.  There were competing teams that were working on this task.  WebDav had a team, led by Russ Simpson, working on a very basic hotmail like experience.  The architecture of this version was the most interesting part.  It was scalable and fast because it was actually built into the Exchange store process.  Bob Gering, Ward Beattie, Iain McDonald and I were on the CDO (Collaboration Data Objects) team building a version with DHTML controls on an alpha version of IE5.  Management fixed the redundant effort issue and joined the two teams together with Ward leading the way.  It made perfect sense to combine the efforts of great plumbers along with great painters. 


The first DHTML prototype for OWA was written on top of a pre-beta version of IE5.  IE5 was such a huge improvement.  IE4 was a great step forward and we did evaluate it but IE5 had many other built-in technologies that let us improve the user experience.  The IE5 browser could certainly absorb xml but making a DAV request was impossible from the browser, so we added an ActiveX control to the prototype that made it possible to make DAV requests such as SEARCH, PROPFIND, etc…  The OWA prototype was demo’d to Billg and he loved it.  This gave us enough momentum to get a component that we needed to be installed by IE5 that we called XMLHTTP.  XMLHTTP was born and implemented by the OWA dev effort of Shawn Bracewell.  Exchange funded the effort by having OWA development build XMLHTTP in partnership with the Webdata team in SQL server.


XMLHTTP changed everything.  It put the “D” in DHTML.  It allowed us to asynchronously get data from the server and preserve document state on the client.   In some cases, OWA is communicating with multiple servers to update the navigation document.  XMLHTTP was not just a self serving effort. We knew that eventually this component would be discovered and used by other web developers that wanted to build rich applications but we just didn’t know when they would discover it.  Oddpost appeared about a year or so after we shipped Exchange 2000.  This application really pushed the limits and used similar techniques found in OWA.  The Oddpost team deserves credit for moving the web forward also.  They did a fantastic job harnessing the power of IE 5.x.


In Exchange 2003 we took it up another notch by asynchronously polling the server for new mail notifications and calendar reminders.  We also added spell check that uses XMLHTTP exclusively to retrieve spelling suggestions from the server.


The OWA team’s desire to build a rich Win32 like application in a browser pushed the technology into IE that allowed AJAX to become a reality. 


The OWA team today is one of the most talented in its history.  Each version of OWA makes huge strides in technology and user interface, and the next release is no different, you’re going to love it.


Jim Van Eaton

Comments (11)
  1. Olivier Hault says:

    I will like to see the next OWA release written for a new extensible and well documented "front end" framework build on top of ASP.NET (or even better XAML)

  2. Adam Gates says:

    Thank you! OWA has been consistently the VERY BEST of E2K and E23k has to offer. Outlook is now completely available via the browser. Wonderful work!

    Now time for Word and Excel!!!

  3. Rialtus says:

    Curious question – the intent obviously was to ensure that OWA worked well with IE on Windows, and that’s just fine being it’s Microsoft. But there is a significant goodness when using "alternate" browsers (Netscape, Mozilla, etc.). Can you elaborate on the thought process that went on in addressing these broswers, as well as what difficulties you had in dealing with a feature rich browser like IE while providing basic functionality to the alternates?

  4. Anonymous says:

    My dev lead Jim has a nice history of OWA on the Exchange blog.  He talks a bit about the early…

  5. Jim Van Eaton says:

    We had to almost provide two codebases to support both experiences. One for the rich IE5+ browsers and another for the alternative browsers. This is one of the weaknesses of developing rich applications that many of the AJAX developers discuss. We decided to take a more low risk approach and try and reach as many browsers as we could with the OWA Basic experience. Going forward, this strategy may change since other browsers have evolved and market conditions change. I think this topic deserves a separate blog so stay tuned.

  6. Klaus H. Probst says:

    I’m sure Jim will elaborate on their efforts to cater to "alternative browsers" if you point out a shipping browser that could actually compete with IE5 in 1998/1999.

    BTW Jim – great entry. I like reading these ‘once upon a time’ blog posts very much.

  7. Anonymous says:

    I’ve been following Ajaxing for a year or so (since Gmail appeared) and am amused to discover that Microsoft invented it for Outlook Web Access in 1998. Microsoft is also taking it further with its Atlas project: The Atlas Client…

  8. Anonymous says:

    Microsoft and AJAX

  9. Amir says:

    I wanted to find out why only Basic Experience of OWA is available on all browsers on Mac? I know they are referred as down-level clients but never have seen a good detailed description of why Premium experience can’t be provided. I would need a feature list (I know ActiveX controls don’t work there, neither XML, but need mroe specific info like why they are necessary and which features in Prem. OWA depend on these underlying feature-set) which is not available in Mac browsers which hinders provision of Premium experience. If someone already know of some public resource, please point me to that. Thanks!

  10. Gergana says:

    Your blog is very interesint

  11. Anonymous says:

    关注ms的Ajax行为。

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