I think user Go Daddy's answer was correct, but I'll write up more succinct instructions that I followed to get the forwarding to work for me. I don't know why others are suggesting wwwizer, because GoDaddy uses a 301-redirect too (but maybe it didn't used to?). By the way, this answer isn't specific to Amazon's S3 -- it simply requires you have the "www" CNAME record set correctly.
- Login to GoDaddy.com.
- Click on My Account.
- Click on the Domains product, and click the Launch button next to your domain.
- In the Domain Information section you should see "Forwarding: Off". Click the Manage link next to it.
- A Forwarding and Masking dialog box should come up. Under Forward DOMAIN.COM to enter "www.domain.com".
- Click the OK button.
The forwarding kicked in for me within maybe half an hour.
To note, in the dialog box you can change it to forward either "http://" or "https://". I only needed it for "http://", so I'm not sure if GoDaddy will forward both SLL and non-SSL at the same time.
Also, if you're curious, if you click on the Advanced Options link in the Forwarding and Masking dialog box, it should be defaulted to "Forward Only" and have the redirect type set to permanently forward your domain (which is what gives the 301-redirect).
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