Just add your email to "Approved Personal Document E-mail List" under your kindle settings https://www.amazon.com/gp/digital/fiona/manage/ref=ya_14#pdo... Then you can sync all your books through mail. Set up a Tasker-profile to automate the copy-process of all epub/mobi/whateverfileextension to the folder of your choice on your Android.

Or setup a spideroak sync folder for the ebook-folder on your android, and just sync your non-amazon books through spideroak.

You can sync non-Amazon books by sending them to you@kindle.com. If you are using something like Calibre it's very simple.

Thanks for this. I knew about the email, but never thought of using it for syncing multiple devices.

Are you sure that this also syncs on your Android Kindle?

It never works on my mobile for some reason.

I have never gotten anything except Amazon purchases to sync to my Android Kindle app. I can manually copy .mobi (and I think .azw) files to my Android and the Kindle app will read them, but there's no Whispersync between devices except for official Amazon purchases. It's the same with my iPod Touch but not many people realize you can manually copy books to the Kindle app.

Didn't know that, thanks!

Have you discovered the (relative) joys of Calibre?

http://calibre-ebook.com

It's not perfect, but it's very good and much nicer than doing it manually. Especially for managing collections. Regularly updated too.

I've only used it for converting books into Kindle format, will try to learn more about it's capabilities. Thanks for the suggestion.