he borrado ini_set("SMTP","localhost"), he modificado a $_POST; el error continua, he visto que debo configurar el php. ini amm y esta asi:
[mail function]
; For Win32 only.
SMTP = agnprincipal
smtp_port=25
; For Win32 only.
sendmail_from =
[email protected]
; For Unix only. You may supply arguments as well (default: "sendmail -t -i").
;sendmail_path =