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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
up vote 13 down vote accepted

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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