"I have about 4 years of email in Outlook and I want to upload it all into my new Gmail account. I suppose I could forward all my mail, but there's got to be some other way of getting it in there. How can I move my Outlook mail messages to Gmail?"
There are several software solutions for helping you migrate from Outlook or Outlook Express to Gmail's online storage. I've used a couple of utilities to do this in the past, but my most recent attempts with these tools failed. Gmail seems to have changed settings making Google Mail Loader and gExodus both fail. Then I remembered another handy way of moving mail - using IMAP as a means of syncing email between two accounts, which I used to do as a method of access my mail across multiple computers. Here's the safest way to make the IMAP transfer work.
Enabling IMAP in Gmail
Step one of the Google migration is to enable IMAP in the Gmail interface. To do this, first click on the Gmail Settings link (at the top right of the page) after logging into Gmail from your browser. Next click the Forwarding and POP/IMAP link and scroll down to enable IMAP. Save your settings change.
Adding Your Gmail Account to Outlook
Next you need to add your Gmail Account to Outlook as an IMAP account. Google provides a good list of steps for doing this right below the IMAP toggle, but I'll cover it here as well.
From the Outlook menu choose Tools > Accounts and create a new account. Input your name, followed by full email@example.com address and password. Be sure to check the box to manually configure server settings or additional server types.
Make sure the account type is set to IMAP.
On the Advanced settings you need to set the incoming IMAP server to 993, with SSL encryption. The Outgoing SMTP server needs to be set to 587 with TLS encryption.
Making a copy of your Outlook Email
After you setup IMAP access for your Gmail account, you can start adding mail to it. Select a folder in your Outlook Personal Folder that you want to add to your Gmail (like Sent Items, for instance), right-click the folder and choose Copy (Do Not drag and drop or you will alter your Outlook folder hierarchy).
This last part requires patience and is best done at a time when you don't need Outlook for awhile. The sync process can take a very long time if you have lots of mail. For the large folders in your Outlook, save this for something you do before quitting for the day, so you aren't frustrated by an inbox that's busy.
When it's finished copying, you will get an error message like the one below because Gmail doesn't use a folder hierarchy. This is normal. What was a folder to you in Outlook will now be a Label in Gmail.
Finding Your Outlook Mail in Gmail
After the sync is complete, you may wonder why you can't easily see your Outlook mail in Gmail. That's because Gmail has it conveniently sorted away by Label in the the All Mail section. If you scroll down the left hand side of the Gmail Web interface, you should see a list of Labels like the one to the left of this paragraph. Clicking on any one of those labels in Gmail will reveal email messages with that label (all the mail that is in the folder of the same name in Outlook).
Cleaning Up Gmail and Finding Your Mail
As you can see, the Labels aren't necessarily very clean when going from Outlook to Gmail. What was once a subfolder of my inbox with podcasting related mail, now has the unfortunate label INBOX/Podcasting. This is easily fixed by clicking Edit Labels, and renaming each of the labels to something less cumbersome.
If you had a bunch of folders imported to Gmail, this may take a couple of minutes, but it gets the job done and you only need to do it once.
Once you get everything moved to Gmail, you can safely close the IMAP account in Outlook without having any impact on what's stored in Gmail, making all of your old Outlook messages instantly available anytime you log into Gmail in the future.