Response Code,Response Types,Commands,Reference LOGIN-DELAY,-ERR,"USER[1], PASS, APOP, AUTH",[RFC2449] IN-USE,-ERR,"PASS, APOP, AUTH",[RFC2449] SYS/PERM,-ERR,All commands,[RFC3206] SYS/TEMP,-ERR,All commands,[RFC3206] AUTH,-ERR,"Any authentication command including AUTH USER [2], PASS, or APOP.",[RFC3206] UTF8,-ERR,"LIST, TOP, RETR",[RFC6856]