PGP key retrieval in mutt

[Nick Willson <nick@nickwillson.com>]

I've been using mutt to read and verify signatures on encrypted and
signed messages.  Provided the sender's key is on my keyring, the
mutt/gnupg combination works very well.

If the sender's key is not on my keyring, gnupg reports
"gpg: Can't check signature: public key not found".

One way to fix that, from an [1]earlier thread, is to add
"auto-key-retrieve" to the list of keyserver-options in my
~/.gnupg/options.  However, that means that gnupg will attempt to
retrieve the key for every sender of signed messages that I open in
mutt.

Instead, I would prefer to be able to tell mutt to tell gnupg to
retrieve a specific key, while viewing a message from the key's owner
in the pager.  How can I do that?

1. http://lists.debian.org/debian-user/2003/debian-user-200301/msg04806.html

-- 
Nick