Here is the simplest solution I found to taking a backup of your gmail. The only glitch is that the mirror account will of course be a perfect image only if you set up the forwarding from day one :-(

I had to use gmvault (gmvault.org/) to make a copy of my gmail; it was quite doable.

Pasted from http://www.webmonkey.com/2008/11/simple_solutions_to_help_yo...

"Create some backup accounts — This one is so obvious I’m always surprised to hear that not everyone does it. Gmail is free and lets you have an unlimited number accounts… so open a second one. Mine is just my usual account with .bak appended to the username. Once that’s set up, login to your primary account and either enable forwarding for all messages (Settings >> Forwarding and POP/IMAP) or create filters to only forward the messages you really care about. Then just send those messages on to the backup account.

I use my main Gmail account to manage five e-mail addresses, so I used the filters method and only back up a couple of them (the others are already backed up on the original domain’s mail server). I also have the forwarding set up to pass messages along to a Yahoo Mail account, an account on my own server and even a good old Hotmail account (or Windows Live Mail as it’s known these days).

This setup is like a good investment portfolio, think of it as e-mail diversification — your’re hedging your bets by spreading your mail around to several servers. If something goes wrong on one account, just login to another. I don’t login to the other accounts much, so they aren’t as carefully filtered, organized and de-spammed as my main Gmail account, but at least my mail is there"