Note, if you are using the gpg.el you must make sure that the
directory specified by gpg-temp-directory have permissions
0700.
Creating your own key is described in detail in the documentation of your PGP implementation, so we refer to it.
If you have imported your old PGP 2.x key into GnuPG, and want to send
signed and encrypted messages to your fellow PGP 2.x users, you’ll
discover that the receiver cannot understand what you send. One
solution is to use PGP 2.x instead. You could also convince your
fellow PGP 2.x users to convert to GnuPG.
As a final workaround, you can make the sign and encryption work in
two steps; separately sign, then encrypt a message. If you would like
to change this behavior you can customize the
mml-signencrypt-style-alist variable. For example:
(setq mml-signencrypt-style-alist '(("smime" separate)
("pgp" separate)
("pgpauto" separate)
("pgpmime" separate)))
This causes to sign and encrypt in two passes, thus generating a message that can be understood by PGP version 2.
(Refer to https://www.gnupg.org/gph/en/pgp2x.html for more information about the problem.)