I've installed Postfix and configured it using this tutorial: http://www.unixmen.com/activate-and-...ntos-and-rhel/
and can successfully send emails from the command line using something like this: echo "test email" | mail firstname.lastname@example.org
I've also set (in the php.ini file) sendmail=/usr/sbin/sendmail -t -i and 'sendmail' is a symlink that points to /usr/sbin/sendmail.postfix, yet it appears the emails are still not being delivered via the web form. Again, they are successfully delivered when testing via the command line, but not when sent through the web form. Here is a link to the php FormToEmail that I'm using (and I've used before on other sites, hosted elsewhere).
(text file of the actual code, I'm using it as-is, but of course with my email address, etc inserted (same php file I used when hosting the site on windows machine, so I know it's not faulty)