First of all, your question is valid, and you can ask questions about MS Exchange in our forums, and are encouraged to do so.
Yes, these are The UNIX and Linux Forums, but that does not mean we do not welcome those who are using other operating systems.
Personally, I prefer UNIX-based mail systems because I prefer open systems to closed systems; but it would be great to see an excellent UNIX/Linux mail system with integrated calendar.
In fact, when I used to consult for many large companies, the single biggest reason they used MS Exchange was for the integrated calendar functionality. Business people like their email and their calendars tightly connected, and this has been a great success of MS Exchange (in addition to their LDAP implementation).
In closing, I would like to remind everyone that we don't simply bash Microsoft or other operating systems in these forums and it has been a long standing violation of our forum policy to do so.
Yes, MS Exchange might be "bloatware" to some; but for countless large businesses, including most of the largest organizations in the US, MS Exchange, with Calendar and LDAP integration, is the backbone of the business operations. What is important is what "users" like, not want "older system admins" (like us) think