How to implement a "send to kindle" link?

I'm trying to find out how to create a link that will send the current page/article on my site to a users Kindle device. I haven't been able to find much about it, but I know it can be done because I see it here: http://openlibrary.org/works/OL258709W/King_Henry_VI and Instapaper offers this functionality, see image. Does anyone know how to do this, or even where to start?

I've seen other posts asking this question, but they were from a while ago and at the time it wasn't possible so there were no answers, now it's possible.

Each registered Kindle has an associated email address. Users can email documents to this address to copy them to their Kindle device and to Amazon's associated cloud storage.

However, by default only the email address associated with the user's Amazon account is whitelisted. You must ask the user to add your email address to their Approved Senders list. Once that's done you just need their Kindle email address and you're good to go.

Each Kindle email address has two variations: @kindle.com and @free.kindle.com. The @free.kindle.com will only transfer documents over Wi-Fi, so that the user is not charged. If you use the @kindle.com email address, it may instead be transfered over 3G at a cost to the user. They can configure their settings to disallow this, but you should be careful not to send documents to this address unexpectedly.

Instapaper's interface is a good example of how this could be done:

Although this has been offered to American Kindle customers for a long time, the international support has been poorer. Until recently this wasn't support in Canada at all, even for wi-fi transfers. I don't know where this is and is not currently supported.

For more details, such as the supported formats, please see the Amazon support document Kindle Personal Document Service.