Why are some people not receiving the confirmation emails?

Some email services (like AOL, Hotmail, and a few others) do not accept mail sent from the PHP mail() function. So, people who sign your petition with an email address from one of these providers may not be able to receive a confirmation email. To get around this problem, try installing the WP Mail SMTP plugin which will redirect calls to the PHP mail() function through your webserver’s SMTP configuration.