Yes, in calibre go to Preferences ==> Sharing ==> Sharing books by email.
Add your send-to-kindle email address (if you don't know it, it is listed at
http://amzn.com/myk) to the list on top, then configure your own email address on the bottom.
calibre will email the books using your email address as a relay (make sure you have allowed it in MYK) and you can send books using the dropdown from the Connect/Share toolbar icon.