ExSP33 - I cannot see why you cannot just do a rolling back-up (daily?) of the relevant email store folder to either another internal or an external drive? I did that with OE for years, over-writing weekly each email store folder and am now doing it daily with Outlook.
To 'select' which emails you want to back-up will, of course, entail selection of each email one by one unless you copy them en block to a 'hold' folder and back that up.