-`C-c C-m s p` and `C-c C-m c p`. To sign outgoing mail by default, use the
-`message-setup-hook` in your `.emacs` file:
+`C-c C-m s p` and `C-c C-m c p`.
+
+In Emacs 28 you will be asked whether to sign the message using the
+sender and are offered to remember your choice. In Emacs 27 you will
+get a slightly misleading error and have to manually add the following
+line to you init file. Older Emacsen just do this unconditionally.
+
+ (setq mml-secure-openpgp-sign-with-sender t)
+
+To sign outgoing mail by default, use the `message-setup-hook` in your
+init file: