What a stupid question! I've never understood why IBM played along with Microsoft's game of comparing those products. At school, kids learn you can't compare an orange to an apple, although I don't mean here that some marketing managers didn't go to school for long enough.

More seriously, how does one compares an application server (Domino) that does mail, Web serving, LDAP, synchronization of databases, database server, etc., to a mail server (Exchange) that does mail only?

So, although I keep thinking that the comparison is nonsense, let's try to compare the few basic features that can be evaluated between the products. Here's my analysis and some comments.

Mail routing
Domino shines in this domain. It's way more powerful, scalable, user friendly and reliable than Exchange.

Any Notes client with sufficient access rights can remotely manage mail stored in a Notes application, in any domain. None of this is in Exchange, with mail stored on disk and hardly manageable.

Moreover, Exchange is based on an unbelievable stack of protocols and bricks of heterogeneous code (i.e., .Net framework, AD, COM, DCOM, WMI, Security layer, roles, and so on). A remote access protocol (NRPC) and low level APIs are basic design elements of Domino since V1. Nothing like this is in Exchange, where remotely accessing servers in different domains to perform administrative tasks is a challenge.

After discussing this point with Redmond's Microsoft experts, I came to the conclusion that there's just no proper software architecture and protocol allowing this. Pieces of code are currently added here and there to mask this lack, but the results so far didn't convince me at all.

Domino supports multiple platforms when Exchange 2007 is limited to Windows 64-bit (the 32-bit version is only for test and not supported in production).

In my opinion, the way mail is processed in Notes is just brilliant. My only serious concern is about the fact that Domino is still supporting its own proprietary and outdated protocols (NRPC and Rich Text) for mail. This will be the subject of another article.

Conclusion
Domino is leading -- by far.

Rich client access
Outlook is easier to handle partly because it contains less features. Also, Microsoft makes a less-full-featured client available for free (and many Exchange hosting providers offer the full version of Outlook for free), Outlook is widely deployed in schools by Microsoft, and the Express/Windows Mail version is available by default in Windows. However, I'm not going to open here the complex debate about the rights for Microsoft to provide a default mail client, media player, or browser in their own operating system.