Maybe this will help if you didn't already know about it.
You should also be aware of the following:
Use the @free.kindle.com address for your kindle or you'll get charged $$
When setting up the email address in Calibre there is a portion for which email address Calibre sends the files from, for example
johndoe@someemail.com You'll need to log into your amazon account and make sure
johndoe@someemail.com is added to the list of addresses allowed to send emails to your kindle.