IE like Crypto AG:
In 2020, it was revealed that the Swiss company, Crypto AG, which provided secure communications services to ~120 governments throughout the 20th century, was secretly ran by the CIA and West German Intelligence. The CIA and later NSA were able to read encrypted communications for many countries such as Saudi Arabia, Iran, Italy, Indonesia, Iraq, Libya, Jordan and South Korea.
for email, the protocol itself is insecure by design. if using it for actual communication you should use something like pgp encryption on top. even proton receives your mails in plaintext, though they claim to store it encrypted afterwards.
get your own domain and use it instead of the provider’s domain, this way you can easily change email providers later on.
also btw, proton doesn’t support imap/pop (afaik)
Yes, I intend to use my own domain name when I switch.
For IMAP, it looks like there are bridges for both Proton and Tuta that I can run locally.