from what i can see everything looks to be configured correctly.
There are a few questions from my initial reply you have not answered though:
I can see from your code, that the smtp server address are left blank, like i said, in some cases this is fine, in others you need to enter an smtp server address, you would need to check with host to see if an SMTP server address is required or not when sending an email using a php script, and if it is required, they will be able to tell you what address to use.
in the code, i see the from address you are using is firstname.lastname@example.org, is this a valid address for your domain?
i see that this option has not been checked, you may need to, again, you need to double check with the host to determine if this option is needed or not.