send mail error

hello, i face a problem with send mail via php. i have a server with ms IIS and i have not access to php.ini how i send a email with php script with auto add the sendmail_from into php.ini ? PS. i write a php script to send email but i receive the follow error message mail(): "sendmail_from" not set in php.ini or custom "From:" header missing in *....... *please advise Thanks Tassos