For the Psiphon mail responder, we configure Postfix with `smtp_tls_security_level=verify` and `smtpd_tls_security_level=encrypt` (with three "may" domain excep

For the Psiphon mail responder, we configure Postfix with `smtp_tls_security_level=verify` and `smtpd_tls_security_level=encrypt` (with three "may" domain exceptions, unfortunately). So, the email should be encrypted through the ISP. Of course, if your ISP is also your email provider (get a new email provider), then your ISP will be able to see and modify your email. We also sign our apps and provide detailed instructions for verifying the authenticity of them: https://psiphon.ca/en/faq.html#verify-psiphon-authentic https://psiphon.ca/en/faq.html#verify-psiphon-authentic (You can't get to that if you can't get to the internet, but it's hard to do much better. We can't email the instructions, since then the instructions could also be modified. But it's entirely possible for some users to be able to load a webpage but not download a 6MB binary.)