I may consider that but it would take a lot of time as there are years of emails. Besides gmail is a good email archive. I keep referring back to old email messages with their pretty accurate search feature. Obviously it may be done in other folder as well but then I would often need to search twice (inbox then archive) and keep maintaining the inbox-to-archive moving of emails which are getting old.

Those are all efforts which seems to me like avoidable and unnecessary. I've found in gmail settings that imap folder sync can be limited to 1000 emails. I'll wipe out emails on the N9 and try to sync again with this limit enabled. We'll see does it help.