Re: Rule number 0
"Someone explain what is so fantastic about MS's offerings?
Apart from being used by many, of course."
For most people, what's fantastic about Outlook is it works with the systems provided by the people who pay them a salary. It's really MS's calendaring system that's the sticking point. You can talk to Exchange just fine with IMAP and do email; you'll even get calendar invitations. But you won't be able to share calendars or see free/busy information for other users, and a lot of companies use that heavily for scheduling.