I noticed that the Google doesn’t provide much help when you have a GoDaddy email address, where a client has emails in the inbox and so on, and you want to move them to Google Apps. Part of the issue is that Google Apps customers don’t have access to the email importer, and if your client has only been using the web interface, there’s no file for you to export with all their message data.
Turns out, the solution is to setup your Google Apps account and set yourself up with your own admin email, so firstname.lastname@example.org, then setup your client’s email, like email@example.com. You can use Google’s Fetch Mail settings to pull mail from GoDaddy into Gmail. However, there’s a catch. You technically have two email addresses that are identical – firstname.lastname@example.org in Gmail and at GoDaddy. And Gmail’s fetch settings won’t allow you to fetch mail from the same address you’re already using.
That’s why you setup you Admin account as the middleman, email@example.com. Fetch mail via POP from GoDaddy into firstname.lastname@example.org. After that’s done, setup fetch (under the Settings > Account, tab) to fetch mail from email@example.com into firstname.lastname@example.org. Emails basically go from GoDaddy, to your Admin Gmail account, then into your client’s email account. That takes care of their inbox and you’ve got mail backups in three places now in case something goes wrong.
To import the sent mail, deleted items, etc., you’ll have to push them into your inbox in the GoDaddy system, then re-filter them when you get them into Gmail. Which sounds daunting, but if you setup a filter and do it in stages, it’ll do it automatically. So, import your inbox first, then your sent items, then deleted items, etc. until you’re done.