Sending Mail with PHP

The most compatible way with either text/plain or text/html:

public function RegistrerSkjema() {
	// Send a confirmation mail.
	$headers = ''.
	"From: ". $_POST['Navn'] ." <". $_POST['Epost'] ."> \r\n" .
	"Reply-To: ". $_POST['Epost'] ." \r\n" .
	"MIME-Version: 1.0 \r\n".
	"Content-type: text/plain; charset=iso-8859-1 \r\n".
	"X-Mailer: PHP/" . phpversion();
	
	$ConfirmationMessage = ''.
	'Navn: '. $_POST['Navn'] ."\r\n".
	'E-Post: '. $_POST['Epost'] ."\r\n".
	'Melding: '."\r\n\r\n".
	$_POST['MerInfo'];
	
	mail('a@domain.com,b@domain.com', 'Domain.com | Contact', $ConfirmationMessage, $headers);
	
	return "<span style='color:green; font-weight:bold; font-size:24px'>Meldingen har blitt sendt.</span>";
}

If you need/want to specify reply parameter to the MTA (e.g. sendmail,postfix etc):

mail('a@domain.com,b@domain.com', 'Domain.com | Contact', $ConfirmationMessage, $headers, '-f noreply@thronic.com, -r noreply@thronic.com');

Additional tip for checking if e-mail is a real format or just BS

if (preg_match("/[a-zA-Z0-9\.]+?@[a-zA-Z0-9\.]+?\.[a-zA-Z0-9]+/", $_POST['Epost']) != 1)
	// Not valid e-mail address format given in contact form.