Thanks @Graham_A .
I've just been reading about exporting emails via Outlook, the client that I use, to a .PST file. As I wouldn't need regular access to my archived mails, I'd probably leave them in the PST file and not bother to import them. However, I need to read up a little more to see how I would go about opening the PST file, if I ever do need to find an old email, and whether that would necessitate me importing the whole lot or not.
I think I'd better do a bit of spring cleaning on my inbox, to rid myself of any that I will never need.
