How to Back Up Your Email Account and Access it Offline IN Android+PC+Mac

In a world where Wi-Fi is everywhere, it's easy to think your email will always be available to you. But even Gmail goes down occasionally. Or your school or work could cut access to your inbox without warning. If you find yourself constantly getting stuck on a plane without Wi-Fi, it would be nice to at least have access to old messages.
If losing your email feels like missing an arm, consider backing up your inbox so you can access it when your web account is otherwise unavailable. You won't be able to access new messages if the internet goes down, but you'll be able to view your entire archive, which is sometimes all you need to keep working.
