mail() function

I am very new at this... I want to use the mail funtion, but instead of using an actual e-mail address for the first argument, I want to pass it a variable that I have assigned to the resulting return of a function. The fuction ends like this : function get_useremail {... $query_data = mysql_fetch_row($result); return $query_data[0]; } I then assigned the function to a variable: $retrieveuseremail = get_useremail ($username, $userid); WHEN I TRY TO USE $retrieveuseremail AS THE FIRST ARGUMENT IN THE MAIL FUNCTION, I GET AN ERROR MESSAGE : Failed to receive in 'C:ThePathToTheDocument' CAN I PASS A VARIABLE HERE? Marlene