It is now possible:
Microsoft makes Outlook for Mac free. After MS Entourage (which I liked) was no longer workable in newer OS versions, I switched to Mail. I had liked Entourage and switching wasn't too bad except that my somewhat-technophobic wife had a period of adjustment (marked with colorful language). After I subscribed to MS Office 365 mainly to get Outlook (which I thought would be just like Entourage) and Word, I found that there were significant differences. I didn't like Outlook's interface and, unlike Entourage, importing contacts from Mail was a huge chore. So, I stuck with Mail (and have learned to like it).
Still, anyone who wants Outlook can now try it gratis.
