I know in some versions of php on windows the email won't send if you include a from or to name. Try leaving the name portion blank and only use the email address in those areas and it may fix the problem. 
This happened to me on ASP as well. I blamed it on the webhost, Network Sol, as other hosts didn't have a problem with it. They also wouldn't send unless the sender email address was in the same domain, that was using CDOSYS.


