I have recently upgraded to to Windows 8.1, and am using Office 365 for the first time. I transferred two email files (.pst) across from my W7 machine, and they are operating as they should (I think). However, I did set up a new account, and that has an .ost file type which I understand means 'Offline'. I guess that this may be because I am using Office 365 and allows the thing to be used in offline mode, which is what I want.

However, I use Acronis to back up, and while it is backing up my .pst files, it is not doing the same with my .ost ones. Should I be worried about this, and is the .ost file somehow backed up into the 365 cloud?