found it! https://yourdigitalrights.org/ :)

https://justdeleteme.xyz/ and https://simpleoptout.com/, there was this one website that had a pre-filled email template too, and it’d remind you to follow up with support, etc. Even while this isn’t for data brokers, it’s good to have these just in general.

I highly suggest Tuta, https://tuta.com/, or other conventional mail boxes like https://mailbox.org/en/

The only thing I don’t like about Session is, it runs on a underlying crypto token, incentivizing the network to keep on going. https://getsession.org/blog/migrating-from-the-oxen-network-to-session-network imo

Mega brain move right here. Combined with a multitude of open source web mail clients and ur golden. SOGo and roundcube my beloved.