Ask HN: Is there something like Sendy but open-source and in Python or Ruby?

Just pay for Sendy or whatever you want or create it yourselve... It's not that expensive and you get the source code of the application.

Also it isn't easy to handle a lot of outgoing mail in a performant way and things can change in the future ( SES, ...), this way. You know Sendy will keep having support :)

$60 with a money back guarantee. You are not going to beat that price. How much is your time worth that $60 is too much?

Yes, there is. It's a Ruby one called Lewsnetter: https://github.com/bborn/lewsnetter