修正しました！
方法は次のとおりです。`
//form validation vars
$formok = true;
$errors = array();
//sumbission data
$ipaddress = $_SERVER['REMOTE_ADDR'];
$date = date('d/m/Y');
$time = date('H:i:s');
//form data
$name = $_POST['name'];
$email = $_POST['email'];
$telephone = $_POST['telephone'];
$enquiry = $_POST['enquiry'];
$message = $_POST['message'];
$apikey = 'key';
$listID = 'id';
//
if (!empty($_POST['newsletter'])) {
$url = sprintf('http://api.mailchimp.com/1.2/?method=listSubscribe&apikey=%s&id=%s&email_address=%s&merge_vars[OPTINIP]=%s&merge_vars[NAME]=name&output=json', $apikey, $listID, $email, $_SERVER['REMOTE_ADDR']);
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$data = curl_exec($ch);
curl_close($ch);
$arr = json_decode($data, true);
}
//validate form data
//validate name is not empty
if(empty($name)){
$formok = false;
$errors[] = "You have not entered a name";
}
//validate email address is not empty
if(empty($email)){
$formok = false;
$errors[] = "You have not entered an email address";
//validate email address is valid
}elseif(!filter_var($email, FILTER_VALIDATE_EMAIL)){
$formok = false;
$errors[] = "You have not entered a valid email address";
}
//validate message is not empty
if(empty($message)){
$formok = false;
$errors[] = "You have not entered a message";
}
//validate message is greater than 20 charcters
elseif(strlen($message) < 20){
$formok = false;
$errors[] = "Your message must be greater than 20 characters";
}
//send email if all is ok
if($formok){
$headers = "From: email.ca" . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";
$emailbody = "<p>You have recieved a new message from the enquiries form on your website.</p>
<p><strong>Name: </strong> {$name} </p>
<p><strong>Email Address: </strong> {$email} </p>
<p><strong>Telephone: </strong> {$telephone} </p>
<p><strong>Message: </strong> {$message} </p>
<p>This message was sent from the IP Address: {$ipaddress} on {$date} at {$time}</p>";
mail("email@gmail.com","New Enquiry",$emailbody,$headers);
}
//what we need to return back to our form
$returndata = array(
'posted_form_data' => array(
'name' => $name,
'email' => $email,
'telephone' => $telephone,
'message' => $message
),
'form_ok' => $formok,
'errors' => $errors
);
//if this is not an ajax request
if(empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) !== 'xmlhttprequest'){
//set session variables
session_start();
$_SESSION['cf_returndata'] = $returndata;
//redirect back to form
header('location: ' . $_SERVER['HTTP_REFERER']);
}
} `
少し変更しましたが、今はうまくいきます！