C открытым кодом (с января 2020).

ProtonMail
"Due to limitations of the SMTP protocol, we have access to the following email metadata: sender and recipient email addresses, the IP address incoming messages originated from, message subject, and message sent and received times. We do NOT have access to encrypted message content but unencrypted messages sent from external providers to ProtonMail are scanned for Spam and Viruses to pursue the legitimate interest of the protection of our users. We also have access to the following records of account activity: number of messages sent, amount of storage space used, total number of messages, last login time."