-This is the authentication method for SMTP AUTH authentication. If
-@code{nil}, @code{smtp-authenticate-type} is used. If
-@code{smtp-authenticate-type} is still @code{nil}, authentication will
-not be carried out.
+This string-valued variable specifies the authentication method for SMTP
+AUTH authentication. You may specify @code{plain}, @code{cram-md5},
+@code{digest-md5}, @code{login}, etc. If @code{nil}, authentication
+will not be carried out.