Ask HN: How to propose a partnership with a startup?

I have a startup and would like to propose a partnership with other startup. How can I approach them?

Is cold email alright? What if I don't know their email? Can I just use Twitter to contact them?

Do I need to present the necessary documents already? Or just a short message about my proposal is enough?

Sorry for too many questions. But yeah, how to propose a partnership with a startup?