I have a GPG key with multiple signing subkeys and I want to force enigmail to sign email with a specified subkey. GPG can be forced to sign with a specific subkey by appending the characted "!" after the subkey id, but engimail does not appear to have any support for that.
1 Answer
Apparently enigmail developers deliberately decided to not support this possibility. A workaround is to manually modifying the file pref.js adding the exclamation mark after the key id specified in lines like
user_pref("mail.identity.id1.pgpkeyId", "0x089380E4!"); This has to be done once for every configured identity.
EDIT I discovered a problem with this workaround: enigmail will use the same subkey for self-encrypting emails. Since the specified subkey will (probably) be a signing subkey (rather than an encrypting subkey), sending encrypted emails will fail if you adopt this workaround.