My main mail client is Outlook 2002. This is no corporate mandate; it's just me here. I've had lots of problems with Outlook over the years and on occasion I've tried to change to another program, but I've always come back. There's just no other program that does all the key things it does. Why not?
We've talked this question over here at Tech Update: Why has the software industry not produced a plug-in replacement for Microsoft Outlook? Few products, even other Microsoft products, get as much bad press as Outlook. Personally I think most of the criticism of Outlook is overstated, but that's not what's important. There's a market opportunity here.
The real key, especially in the corporate market, is to produce a client that supports Microsoft Exchange and is interoperable with Outlook for supporting e-mail, calendaring, and some other groupware features.
Instead, the software industry seems more taken with the notion of replacing Exchange and leaving Outlook in place. Oracle has their Collaboration Suite and Bynari makes a number of server products that support Outlook clients.
It's a bit off the point, but even without looking at how well these products do their jobs, I can recommend that you avoid adopting them for a while. There's no server-level antivirus protection available for them. Viruses don't attack Exchange, they attack Outlook, so replacing Exchange, which has many antivirus solutions available, actually weakens your security situation.
An Outlook replacement, on the other hand, probably strengthens your position, by taking out perhaps the most significant target of virus writers over the last couple of years. But it raises an interesting question: If an Outlook replacement is not as programmable as Outlook it's not as vulnerable to attack, but it's still not as customizable. I suspect this is important to a lot of you.
If you're running Linux or Unix on your desktop you can use Ximian Evolution as an option. I haven't tried it out, but I have to at least admire the fact that they have tried to create a full-function client, even if they have take the path of Outlook-aping (see this picture of Evolution to get a sense of how much it looks like Outlook.) They even have a flexible back-end architecture that has allowed them to ship a Connector for Microsoft Exchange Server. I'm impressed with their ambition, although I don't know how well the product actually works. (For more on Ximian Evolution and Connector, read Ximian Evolution fuels interest in desktop Linux.)
For the Windows platform, there's literally nothing that does even most of what Outlook does. But there is competition for the combination of Outlook and Exchange in the form of Notes, GroupWise and a number of other competitors. And there are lots of mail client replacements like Eudora, but they do nothing more than mail and maybe newsgroups.
How did it come to this? As I think back on the development of such software, nobody even really tried. Netscape made noises about calendaring functions in their client, but they could never quite get the job done. Par for the course there.
There are those who argue that there is no meaningful reason to tie all these groupware functions into e-mail. There's some logic to this, as long as the e-mail and other functions (scheduling meetings, for example) all draw their contact information from a central directory, but there are ways to do that without integrating the programs completely. And yet it seems that integration is exactly what customers want, especially if they also want to script the functions involving e-mail.
E-mail, contact management, and calendaring are such important applications that no amount of Office preloading would stop a third-party from being successful if they made a better product. Not only have they not made a better product than Outlook, almost nobody seems to be trying.
Maybe it's naive of me, but I think maybe the answer will come with Web services. Someday there will be an Exchange.Net, and it will be programmable with Web services. Undoubtedly there will be a version of Outlook that works with it, but it should be easier than ever to write Exchange client programs without basing them on Outlook, and there should be less dependency on Windows too.