mail()

Using php/apache/mysql I am testing an mail script. The script has a .html form which receives the text input and then a .php script to execute the variables in a mail() function. When I publish both files - the .html and .php - to my ISP's server and enter the data and hit submit I receive an e-mail. In my php.ini file I have configured the SMTP to the name of the ISP's email server. However, when testing the same script out locally on Apache Server: I get the form box, enter the data but I do not receive an email. I only use one ISP. Is it possble they have two name servers and that is why I am not receiving an e-mail when testing on Apache Server? Thank you for any help. Best... Tony Ritter