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.
I am annoyed by this too. The big limitation would have had you could not use IMAP as that is remote.
The other issue is implementation. It would be easy to forward or attach or just store unencrypted in an insecure way which may not be desirable. Frankly for what I do I would prefer Thunderbird decrypt on receipt but place all content in a vault. If one wanted to add some more restrictions one could make it hard to forward by accident mail that was originally encrypted.
The big issue with PGP has always been a combination of bad implementations and key distribution.