mc-pgp-fetch-from-keyrings will attempt to fetch a
key from a set of keyrings on the locally accessible filesystem. This
is useful if your organization maintains a large common public keyring
whose entire contents you do not wish to duplicate on your own ring. It
is also useful if you download a copy of the global public ring from the
key servers (see Key Servers).
mc-pgp-fetch-keyring-list controls this behavior.
It is a list of file names of public keyrings which this function will
search, in order, when seeking a key. The default value is
meaning this search will always fail.