https://www.reddit.com/r/privacy/comments/6z6s5u/protnmail_not_what_it_stands_for_anymore/dmu7oih/
https://www.reddit.com/r/privacy/comments/83ju2f/protip_protonmail_is_not_what_it_seems_use_pop3/
Vendors using ProtonMail could be putting their customers at risk, if they are relying on ProtonMail's built in snake oil encryption.
Remember to always use GPG for all dark net related messages.
Vendors using protonmail are looking for a reliable email service. Use PGP and rest easy.