Usage: crypt-hook pattern keyid
When encrypting messages with PGP or OpenSSL, you may want to associate a certain key with a given e-mail address automatically, either because the recipient's public key can't be deduced from the destination address, or because, for some reasons, you need to override the key Mutt would normally use. The crypt-hook command provides a method by which you can specify the ID of the public key to be used when encrypting messages to a certain recipient. You may use multiple pgp-hook's with the same pattern; multiple matching pgp-hook's result in the use of multiple keyids for recipient.
The meaning of "key id" is to be taken broadly in this context: You can either put a numerical key ID here, an e-mail address, or even just a real name.