> Thunderbird would work with Fastmail for encryption using PGP or SMIME (at least I think Thunderbird supports SMIME).
Thunderbird supports SMIME natively, just like most of email clients. But of course there are some usability issues, like you need to enable encryption each time per email, or require it for all emails, there is no middle ground like "encrypt if I have keys, do not encrypt otherwise".
Thunderbird supports SMIME natively, just like most of email clients. But of course there are some usability issues, like you need to enable encryption each time per email, or require it for all emails, there is no middle ground like "encrypt if I have keys, do not encrypt otherwise".