Contact form not sending email

I have developed a contact form and followed the directions given to modify the sendemail.php. Yet, upon testing the page, I get a "Failed to load resource: Preflight response is not successful" error for the sendemail.php file. I have tried this on both my local host set up under MAMP and on my official web host. Neither works. Can you please provide some assistance? Of note, I have also tried the SMTP option you provided without success.

This issue is now resolved.