It is not that easy, but I'm always ready to learn. Outlook, insofar as I am aware, has no facility to back up the .pst file. MS's advice is to manually copy the .pst file to another location and back up that location, in other words, Outlook has no solution; I can work out all by myself that I need to copy it but copying isn't really the same a backing up and anyway, doing it this way means the backup is always out of date.
Moreover, there is no way to automate the backup while the .pst file is open. For example, Memeo backs up my data to an external drive automatically but it cannot deal with the .pst file if it is open in Outlook, which it always is, so, to stop the perpetual error messages, I have excluded it. Windows backup works even less well for .psts, it just says backup failed then you have to dig around and find out why and then try to work out if your .pst file got updated despite the error message. My data is also continuously backed up on the internet via Carbonite but this also cannot backup an open .pst file because it is constantly changing, so I have it back up only the last version of the .pst that was manually copied from the active .pst. Consequently, the .pst backup only happens when I copy it out, and because I only do this intermittently it is always out of date.
Ideally, the .pst file would copy itself to a location capable of being automatically backed up on closing Outlook, then it would be backed up at the next logon, but I can see no way to make that happen.
I haven't come across a way around this, but I am open to suggestion from those who know better.
I don't think Apple will go bust any time soon but just be aware that once your data is in the Cloud in any form there is no absolute obligation for the host to maintain it or to keep it private. Probably, we will all be OK, but, until legislation concerning Cloud data ownership and access is more robust, better to keep your data with you and back it up remotely, not the other way around.