A couple days ago I posted a link to upcoming Outlook Object Model changes and new features, I wanted to go back and note that the Exchange team posted about their developer roadmap as well. This post mentions three new ways of interfacing with Exchange in version 12 that you should be really excited about: web services, agent scripts, and the Monad shell. From what I have seen and heard about E12, I can't help but get excited. The Exchange team has done a great job of listening to the community and delivering product features and enhancements that go a long way towards addressing our wish lists as well as things we never knew to ask for.
...I paid particular attention to the following line about web services in E12, "Our new Web Services will offer remotely-accessible Outlook-compatible business logic for all PIM types." Obviously this sentence is intentionally vague but you should be thinking about a remoteable API that would allow access to Outlook item types like Appointments and Contacts. I don't have specifics on which item types will or will not be supported by the E12 web services, you'll have to keep checking with the Exchange team or my blog to get updates in the coming months.
With the new additions there are things that are being de-emphasized and others that will not be available. Note that WebDAV, CDOEX, and EXOLEDB are the three de-emphasized API's. As they suggest agents will replace CDOEX and EXOLEDB for Exchange server eventing, however Event Sinks will still work against E12.
...It is important to understand the support impact of the word "de-emphasized". From my perspective it means that I will support the use of WebDAV, CDOEX, and EXOLEDB against E12 for entire lifecycle of the product, however the product team will not accept design changes or feature enhancements submitted by me on your behalf regarding these API's. It does mean that these API's will have full break/fix support in which the product team will provide with hotfixes and workarounds. It also means that E13+ will most likely not ship support for these API's.
For every new day there is one that has drawn to a close and with that in mind there are a couple existing API's and developer features not continuing to E12. They are listed in the blog post as well. The most common technologies listed here are Web Forms (custom ASP forms in OWA, much like custom forms in Outlook) and CDOWF (Workflow for Exchange apparently will not be supported in E12). The other technologies are less common but I don't doubt that this will impact many of you.
...Most of the technologies listed here that are going away in E12 will have a much better alternative or had some supportability issues to begin with. For example, ExWin32 or the M: drive, isn't considered an API or development technology at all, we don't support doing any development against it in the current versions of Exchange. Web Forms in OWA are almost always better handled through a custom web application or Sharepoint. Workflow application in Exchange can be better served through BizTalk or the new Windows Workflow Foundation...