If you want to use PGP, you can specify
Pgp: [ E | S | S<id> ]
``E'' encrypts, ``S'' signs and ``S<id>'' signs with the given key, setting $pgp_sign_as permanently.
If you have told mutt to PGP encrypt a message, it will guide you through a key selection process when you try to send the message. Mutt will not ask you any questions about keys which have a certified user ID matching one of the message recipients' mail addresses. However, there may be situations in which there are several keys, weakly certified user ID fields, or where no matching keys can be found.
In these cases, you are dropped into a menu with a list of keys from
which you can select one. When you quit this menu, or mutt can't
find any matching keys, you are prompted for a user ID. You can, as
usually, abort this prompt using ˆG. When you do so, mutt will
return to the compose screen.
Once you have successfully finished the key selection, the message will be encrypted using the selected public keys, and sent out.
Most fields of the entries in the key selection menu (see also $pgp_entry_format) have obvious meanings. But some explanations on the capabilities, flags, and validity fields are in order.
The flags sequence (%f) will expand to one of the following flags:
R The key has been revoked and can't be used.
X The key is expired and can't be used.
d You have marked the key as disabled.
c There are unknown critical self-signature
packets.
The capabilities field (%c) expands to a two-character sequence representing a key's capabilities. The first character gives the key's encryption capabilities: A minus sign (-) means that the key cannot be used for encryption. A dot (.) means that it's marked as a signature key in one of the user IDs, but may also be used for encryption. The letter e indicates that this key can be used for encryption.
The second character indicates the key's signing capabilities. Once again, a ``-'' implies ``not for signing'', ``.'' implies that the key is marked as an encryption key in one of the user-ids, and ``s'' denotes a key which can be used for signing.
Finally, the validity field (%t) indicates how well-certified a user-id is. A question mark (?) indicates undefined validity, a minus character (-) marks an untrusted association, a space character means a partially trusted association, and a plus character (+) indicates complete validity.