

The other is that Send Later needs to then be able to encrypt their contents before placing the message into the Outbox, when its scheduled time arrives. One is that Thunderbird needs to allow some programmatic access to the raw content of those messages, presumably just by allowing you to store them unencrypted in Drafts. Two things will need to happen before this really has a workable solution. That makes them both unreadable to your recipient, and also blocks Send Later from opening them without user interaction (note there might be some way for send later to open them if you don't have a passphrase on your private key, but that's not really a solution). So instead Thunderbird encrypts those messages with your own public key.

This wouldn't be a problem if Thunderbird encrypted Draft messages using the recipient's public key, but the point of encrypting draft messages is that you can open them up again and continue editing them.
