Haha, welcome to the club @ninagruenewald! Now imagine my confusion, figuring out how to do it right for something as massive as The Open Mic. I literally lost all sleep over this (just going over all the little things I need to do).
By the way, have you seen this post by Pieter Beens?
Might be very handy.
If you also add people to a marketing newsletter when they contact you on your site, that's a whole other story and you'll need a consent for that too (like a 2nd checkmark in your contact form saying, Yes, you can send marketing emails to me).