allora:
questi sono tutti i dati del phpinfo.

SMTP localhost localhost
smtp_port 25 25
Path to sendmail /usr/sbin/sendmail -t -i
mail.force_extra_parameters no value no value
sendmail_from no value no value
sendmail_path /usr/sbin/sendmail -t -i /usr/sbin/sendmail -t -i

cosa potrebbe essere?