How do I move my emails from one provider to another?

The fundamental problem is this: you have hundreds or in some cases thousands of emails sitting in you folders on a web-based service like Hotmail, Gmail or any of several others - either free and paid. When it comes time to change to a different service, there really is no consistent way to bulk move those messages.

You could forward them all, one by one, sending them from your old account to your new account's email address. Not only is this a lot of time and work, but it also alters the emails slightly, adding a "Forwarded", header for example.

If the old service supports "pop3" access, and the new service supports remote account retrieval via "pop3", you can at least move the contents of the inbox this way. For example, Hotmail added the ability to access your inbox via POP3. While that's typically intended for downloading to a desktop email program, it can be used to copy mail as well. GMail has a "Check mail using POP3: (Get your mail from other accounts in Gmail using POP3.)" as an option. Simply configure that to access your Hotmail account, and in theory the contents of your Hotmail inbox should show up in GMail.

Using Hotmail and GMail is just an example; any two services would do, as long as they both support the appropriate part of the POP3 protocol.

The other approach, and the one that I actually prefer, is not to use webmail unless I'm actually traveling and away from my computer. I prefer a desktop email program like Outlook or Thunderbird or any of dozens of others. This way not only do you continue to use the same email program constantly, but all of your email, regardless of where it comes from, is stored on your machine and is under your control. Naturally, you need to make sure you're backing up, but when time comes to change email providers, there's nothing to move. It's all in the same place. A few account configuration additions or changes, and your email continues to arrive at, and be stored on, your PC.

If your old web based service provides POP3 access, you can actually download your inbox into a desktop program at any time. (It's actually my recommended approach to backing up webmail, if even if you rely on that for your primary access.) Then, just make sure that your new service also provides POP3 and SMTP access (you mentioned GMail, which does), and use that to access the service.

Big Fat Caveat!

Sadly, nowhere above did I mention folders or contacts.

Unfortunately, I'm not aware of any way to move or preserve folders of emails across services, or even downloading them into email clients. Similarly, contacts are another point of pain, as there's no standard way across all these services to share or migrate your address book or contact list.

Again, this is another reason I prefer my desktop email program.