First and most obviously, these are the UNIX forums, and Exchange is a Windows product.

The UNIX philosophy is that programs should do one thing and do it well. A mail server should be a mail server -- not a bloated all-singing all-dancing time management monstrosity. Go down that path too far and you get Lotus Notes, a mail program so baroque that nobody can tell you what it actually does in full, or why, without beginning to drool and twitch.

There's a lot of good reasons to not want to use Microsoft products, besides. The upgrade treadmill is one. The ridiculous prices are another, even as we watch licenses grow more and more expensive plus less and less useful. The long history of legendary security goofs, and continuing security issues even now, is a third.

As an aside, vanilla sendmail is pretty obsolete now. There's other compatible options like postfix.