How do i automatically send ebooks to my Kindle?
On the Mac You can use automator to set up a folder action for this. I added a filter for mobi files use this folder action directly with my Downloads folder. The Script consists of three actions:

The first action would be this applescript:

on run {input, parameters}
    set theFile to first item in input
    set theFileAsString to theFile as string
    if theFileAsString ends with "mobi" then
        return theFile
    else
        tell me to quit
    end if
end run


Second, you need a "New Mail Message" action with your name@kindle.com email address. Be sure, that the sending mail address is trusted in your kindle settings of your Amazon account.

Third, you would use the "Send Outgoing Messages" action.

Be aware that this script takes only the first mobi file when you drop multiple files at once into your folder.