Onion http://rurcblzhmdk22kttfkel2zduhyu3r6to7knyc7wiorzrx5gw4c3lftad.onion/
This free email provider is not for everyone. Sometimes a Cockmail address is not accepted to register something. Sometimes, though not often, another email provider may indiscriminately block email from Cock.li. Afaik Cock.li<->Proton, Cock.li<->Tuta work.
PS: Admin, Vincent Canfield @vc@shitposter.club
No invite is necessary to sign up, so you don’t need to give invites. There used to be INVITE menu item, but it’s gone.