-int mutt_cmp_addr (const address_t * a, const address_t * b);
-int mutt_cmp_list (const string_list_t * a, const string_list_t * b);
-int mutt_cmp_env (const ENVELOPE * e1, const ENVELOPE * e2);
-int mutt_cmp_body (const BODY * b1, const BODY * b2);