I am one of those OCD people who have kept every email since the early 90s. I have them in a range of different formats from early Outlook to Windows Live Mail. For two years or more I have been a Mac convert and managed to import the more recent emails into Mac Mail and build my own archive folders on my Mac.
However, I have also been using GMail for a long time and, similarly, like to keep archives there as well.
My problem is that if I archive messages on Gmail first they disappear from my sync'ed Mac Mail. I thus don't have a Mac-held copy. Equally, if I archive messages on my Mac they disappear from GMail. Apart from advising me not to be so paranoid about losing stuff, is there a way round this?