I\'m having issues sending emails using the php mail() function. I know the php script I have works because I have an identical copy of it on another web-hosting company and it
Whatever the solution, check your mail()'s output.
Most common solution
Ask your hosting company if your current web host has SMTP set up to relay mail from your scripts. If they say "no", then they might have another SMTP host for you to use like smtp.example.com, or you'll have to use another SMTP relay (check with your current e-mail provider).
Alternative
The SMTP server you're talking to might not understand what your script is saying. I've seen situations before where my mail script will work with Postfix but not qmail. This is easily solved by using a third party e-mail library: there are tons out there, but my favorite is Flourish's (http://flourishlib.com/docs/fEmail).