Trouble with mail

Hi,
eg my doamin is example.com
my dns & webserver are on same machine but my mail server with google (I using google apps mail service http: //www. google.com/ a/help/intl/en/admins/editions.html ).

I am facing a problem:

I am unable to send a mailt to abc @ example.com from xyz @ example.com using php script from example.com webserver.
but I am able to send a mail to any domain Id using php script of example.com.

or same domain using ( to abc @ example.com from xyz @ example.com ) using google app interface.

In short : Unable to send mail with in same domain using php script.



Please help me ??