* Signing and encryption:: Signing and encrypting commands.
* Using S/MIME:: Using S/MIME
* Using OpenPGP:: Using OpenPGP
+* OpenPGP Header:: Adding OpenPGP headers to messages.
* Passphrase caching:: How to cache passphrases
* PGP Compatibility:: Compatibility with older implementations
* Encrypt-to-self:: Reading your own encrypted messages
@code{mml-default-sign-method} determine which variant to prefer,
@acronym{PGP/MIME} by default.
+@node OpenPGP Header
+@subsection OpenPGP Header
+
+The @samp{OpenPGP} header can be used to provide information about the
+sender's OpenPGP key. This is a formalisation and modernisation of
+the non-standard @samp{X-PGP-Key} (etc.) headers that have been in use
+for a long time. For more details, see
+@uref{https://tools.ietf.org/html/draft-josefsson-openpgp-mailnews-header}.
+
+@vindex message-openpgp-header
+To use this in Message, say:
+
+@lisp
+(add-hook 'message-send-hook 'messasge-add-openpgp-header)
+@end lisp
+
+Then customize the @code{message-openpgp-header} variable according to
+your PGP setup. The variable is a list of the key ID, the key URL or
+ASCII armoured, and the protection preference, one of
+@samp{"unprotected"}, @samp{"sign"}, @samp{"encrypt"} or
+@samp{"signencrypt"}.
+
@node Passphrase caching
@subsection Passphrase caching