Microsoft ended free custom domain support earlier this year [0]. To use custom domains with Outlook.com, you either have to have already configured Outlook to use a domain name or pay $5/user/month for Office 365 [1].
You don't need a key for downloading. For uploading, you use an access/secret key pair from https://archive.org/account/s3.php You then add that to the ia tool with "ia configure".
0: http://microsoft-news.com/microsoft-ends-custom-domain-suppo...
1: http://products.office.com/en-us/business/compare-office-365...