Email a form using PHP works intermittently

Question

Hello all,
I'm using DW CS6/ Win 7. I have created a simple subscription form where the user enters their email and the form is emailed to an administrator. Sometimes it works and sometimes it doesn't and I have no idea why. Occasionally I  receive the email after a delay of several minutes and sometimes it never arrives. The webpage is here www.sanbenitoolivefestival.com/contactus2.php , below is the script , I've tried in IE and FF, same intermittent results. I'm new to FF/ Firebug but it didn't report any errors that I could see
<div class="subscribe">
    <div class="spacer"></div>
<?php
if ((isset($_REQUEST['email'])) && ($_REQUEST['email'] != " Enter Email Address"))
//if "email" is filled out, send email
    echo "sending mail";
    //send email
   $email = $_REQUEST["email"] ;
   $subject = "SBOF EMAIL SUBSCRIPTION REQUEST" ;
   $message = "Please add my email address to the SBOF email subscription list" ;
   mail("[email address removed by moderator]", $subject,
   $message, "From:" . $email);
   echo "Thank you, we have sent your subscription request";
else
//if "email" is not filled out, display the form
   echo '<form action="contactus2.php" method="post" >
     <em>Stay in touch by joining our email list.                  
      <input name="email" type="text" value=" Enter Email Address" size="42"  class="input" />         
     <input name="submit" type="submit" value="   SUBSCRIBE  " class="button"/>
      </em>
    </form>';
?>
</div>

Answer 1

You are using an extremely insecure technique that lays your form wide open to a malicious attack known as email header injection, which can turn your form into a spam relay.
You should NEVER use unfiltered form input in the email headers. The From header is intended to indicate who sent the email. In this case, it's your website, not the person who fills out the form. If you want the convenience of hitting the reply button in your email program to use the sender's email address, you should use the Reply-to header instead of From.
Misusing the From header like this is one possible cause of your emails not getting through. You should also check with your hosting company to see if they require the fifth argument to mail() to be set. This is normally a string that begins with -f followed immediately by a known email address on the same domain as the server, for example '[email protected]'.
Also, using $_REQUEST is insecure.
Change your code like this:
<?php
if ((isset($_POST['email'])) && ($_POST['email'] != " Enter Email Address"))
//if "email" is filled out, send email
    // make sure the email is OK
    $email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
    // send the message only if the email address is valid
    if ($email) {
        echo "sending mail";
        //send email
        $from = '[email protected]';  // this should be your own email address
        $subject = "SBOF EMAIL SUBSCRIPTION REQUEST" ;
        $message = "Please add my email address to the SBOF email subscription list" ;
        $headers = "From: $from\r\nReply-to: $email";
        $sent = mail("[email address removed by moderator]", $subject,
            $message, $headers);
        if ($sent) {
            echo "Thank you, we have sent your subscription request";
       } else {
            echo 'Sorry, there was a problem sending your request';
else
//if "email" is not filled out, display the form
   echo '<form action="contactus2.php" method="post" >
     <em>Stay in touch by joining our email list.                 
      <input name="email" type="text" value=" Enter Email Address" size="42"  class="input" />        
     <input name="submit" type="submit" value="   SUBSCRIBE  " class="button"/>
      </em>
    </form>';
?>