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I'm quite new to OpenPGP and am just starting to use it with Thunderbird.

When I encrypt a mail with a recipient's public key, using Thunderbird + Enigmail + OpenPGP, and send it, I can find the encrypted mail in my sent-folder. It is possible for me to decrypt (happens automatically) and read it, which is fine, but I wonder; how is this possible? Isn't this ciphertext only decryptable with the recipient's private key? Is it also decryptable with any of my keys (my public or private key)?

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    I'd imagine Thunderbird's local copy (in your outbox) either isn't encrypted, or is encrypted using your key, whereas the copy sent over the internet is encrypted with the recipient's public key. – Polynomial Nov 28 '12 at 9:45
  • @Polynomial Hmm, okay, that makes sense. The copy in my sent-folder is positively encrypted, but then probably with my key. – poplitea Nov 28 '12 at 9:48
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In the normal Thunderbird configuration, the emails are stored the way you send them, so if you send an encrypted email, it's also encrypted in your sent folder. (Note: there may be a way to configure Thunderbird or Enigmail differently, I don't know much about their configuration possibilities.)

Enigmail has an “Encrypt to self” preference (in the Sending tab; extensions.enigmail.encryptToSelf), which is on by default. With this preference turned on, all the emails you encrypt are encrypted for you (with the key configured in the applicable per-identity settings). Unless you've configured Thunderbird in an unusual way, this is what you're observing.

The underlying OpenPGP/GnuPG implementation can be configured for this as well, with the encrypt-to option in gpg.conf.

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    This cleared things up. I find the setting you're referring to as Add my own key to the recipients list under the Sending-tab. – poplitea Nov 28 '12 at 11:28
  • I'm fairly convinced this setting is now completely gone from the UI. – mlissner Oct 2 '14 at 23:38

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