Depending on how you setup Outlook 2016 or more specifically how you setup your account within Outlook 2016 (POP3 / IMAP versus Exchange ActiveSync) your outlook stuff (emails, calendar, contacts) are stored in one of two file formats, either .pst or .ost
These "stores" (the st part of pst and ost) are either "personal" (pst) or "online" (ost).
Perhaps for a better understanding, you might read this
http://www.msoutlook.info/question/802
So basically or perhaps ideally you'd want to configure Outlook 2016 and your associated account as a POP3 style account which will keep everything of importance in your local copy of the .pst file, and.....
That is the file you would want to make sure you backup.
There is no need for a specific, dedicated Outlook backup program as most backup programs will back up a .pst file as long as the file location is included in the backup schema.
IF you're asking for a good, comprehensive and robust backup program, my recommendation is Acronis True Image (use it to create disk images of everything on your physical disk(s))
Shop around and wait for a deal. I just got an upgrade plus a full version for a second computer from Acronis for $20 bucks.
There are other products available that offer similar solutions which might be worth looking into....
https://www.windows10forums.com/threads/please-for-your-own-peace-of-mind.794/
Many people seem to really like Macrium Reflect which I believe has a free version.
I've just always used Acronis and found it very reliable so I've stuck with it.