The default mail mode is now Message mode.
You have the following Mail mode variable%s customized:
\n %s\n\nTo use Mail mode, set `mail-user-agent' to sendmail-user-agent.
-To disable this warning, set `compose-mail-check-user-agent' to nil."
+To disable this warning, set `compose-mail-user-agent-warnings' to nil."
(if (> (length warn-vars) 1) "s" "")
(mapconcat 'symbol-name
warn-vars " "))))))