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I'm trying to set up a send-hook so that gpg encryption is enabled when I send to a specific recipient, but if it's sent to other recipients as well, then encryption is disabled. However, send-hooks seem to fire when a particular recipient is anywhere in the recipient list, regardless of who else is present.

Ideally, I'd encrypt if it goes to foo@bar.com, but not if goes to foo@bar.com, not@this.com, or@whatever.com. The mutt manual says

When multiple matches occur, [send-hook] commands are executed in the order they are specified in the muttrc.

Hence, I put the following in my muttrc. If mail is sent to foo@bar.com, then enable autoencrypt. However, if there is a recipient that is not foo@bar.com, then unset autoencrypt.

send-hook . unset crypt_autoencrypt
send-hook "!~l ~t ^foo@bar\\.com$" "set crypt_autoencrypt"
send-hook "!~l !~t ^foo@bar\\.com$" "unset crypt_autoencrypt"

However, it doesn't seem to work. It seems that send-hooks don't seem to parse each individual recipient separately. Even if I address mail to foo@bar.com, not@this.com, mutt attempts to encrypt it.

Workaround

I can get around this with a very ugly hack.

send-hook . unset crypt_autoencrypt
send-hook "!~l ~t ^foo@bar\\.com$" "set crypt_autoencrypt"
send-hook "!~l ~t [^r]\\.com$" "unset crypt_autoencrypt"

If I send an email to a .com address that has a non-r character preceding, then it won't encrypt. There are obviously lots of …r.com addresses that aren't foo@bar.com, so I have to extend the third line as follows.

send-hook "!~l ~t '([^r]\\.com|[^a]r\\.com)$" "unset crypt_autoencrypt"

This also excludes …r.com addresses with a non-a character preceding too. I just repeat this sequence a few more times.

The major problem with this is that send-hooks don't seem to fire for cc: addresses, making this whole third line moot if the email is cc:ed to not@this.com.

1

In muttrc, use

set crypt_opportunistic_encrypt = yes

From $ man 5 muttrc

crypt_opportunistic_encrypt
      Type: boolean
      Default: no

      Setting this variable will cause Mutt to automatically enable
      and disable encryption, based on whether all message recipient
      keys can be located by mutt.

      When this option is enabled, mutt will determine the encryption
      setting each time the TO, CC, and BCC lists are edited.  If
      $edit_headers is set, mutt will also do so each time the
      message is edited.

      While this is set, encryption settings can't be manually
      changed.  The pgp or smime menus provide an option to disable
      the option for a particular message.

      If $crypt_autoencrypt or $crypt_replyencrypt enable encryption
      for a message, this option will be disabled for the message.  It
      can be manually re-enabled in the pgp or smime menus.  (Crypto
      only)

This also inspects cc:ed addresses for validity. Unfortunately, as per the second-last paragraph, this overrides many useful settings. For example, I have set pgp_autoinline = yes, which is deprecated, but necessary for sending to older clients1, which don't support PGP/MIME.

1 For example, Android's K-9 + APG. AFAIK this is the only FOSS Android email client that reads PGP-encrypted email at all, but only in a limited fashion. (EDIT: K-9 + openkeychain now supports PGP/MIME.)

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