Clients like Thunderbird are great because you have everything stored locally so you can easily search offline. They also support encrypting and decrypting emails in PGP. However, they seem to have the same limitation as protonmail where you can’t search through encrypted emails.
I know that protonmail can’t just store your key at their server since that would defeat the purpose, so the emails are all ciphertext to them right? But in Thunderbird, you already have the key and decrypt everything all the time. So why can’t you skip the middleman in your local machine and store everything locally in plaintext? It’s not less secure since if your local machine is compromised, your private key is also compromised.
Or at the very least give us the option and have a slightly less secure but much more convenient option.
This may be a long shot, but it’s what I do, so it might be an option: Set up a crypto gateway like CipherMail which will automatically decrypt inbound email and sign/encrypt outbound. The result is that your Thunderbird will never get to see an encrypted email, decryption is handled transparently before it hit’s your inbox. Obviously, if you don’t trust your email provider, this is not an option.
This isn’t simple and hence not for everyone, also comes with dependencies on your email provider, but it works flawless for me ever since I set it up. I run my own email server, hence adding in CipherMail wasn’t a big deal.