Is it easy to send data to an FTP server? My first question is just Yes or No.
Mostly No is my guess.
The Agent API currently ONLY exposes an HTTP interface which is an Application Layer Protocol. FTP is a different application layer protocol and so is not currently supported by the agents.
You would need either an FTP implementation done “under the hood” of the Squirrel code by Electric Imp (probably preferred) or an API to the transport layer so you could write your own FTP server in Squirrel which I would guess to be pretty painful.
The reason my answer was mostly No is that you can probably find a service somewhere online that you could send HTTP base64 encoded binary data and then download that data back over FTP - I don’t know any off the top of my head though.