带有下拉列表的PHP联系表单，用于更改电子邮件

我正在处理一个带有下拉菜单的联系表格，以选择特定医生的电子邮件地址。我正在使用模板，在PHP方面没有太多经验。当我将表单上传到服务器时，我收到"警告：array_key_exists（）的参数计数错误"，但我无法查明问题所在。

<link href="css/contactform.css" rel="stylesheet" type="text/css" />
<?php
// Set email variables
$email_to = array('phys1' => 'phys1@xxxxxx.xxx', 'phys2' => 'phys2@xxxxxx.xxx');
if(array_key_exists($_POST['dropdown']))
{
$recipient = $emails[$_POST['dropdown']];
//send email to $recipient
}
$email_subject = 'Form submission';
// Set required fields
$required_fields = array('fullname','email','comment');
// set error messages
$error_messages = array(
'fullname' => 'Please enter a Name to proceed.',
'email' => 'Please enter a valid Email Address to continue.',
'comment' => 'Please enter your Message to continue.'
);
// Set form status
$form_complete = FALSE;
// configure validation array
$validation = array();
// check form submittal
if(!empty($_POST)) {
// Sanitise POST array
foreach($_POST as $key => $value) $_POST[$key] = remove_email_injection(trim($value));
// Loop into required fields and make sure they match our needs
foreach($required_fields as $field) {       
    // the field has been submitted?
    if(!array_key_exists($field, $_POST)) array_push($validation, $field);
    // check there is information in the field?
    if($_POST[$field] == '') array_push($validation, $field);
    // validate the email address supplied
    if($field == 'email') if(!validate_email_address($_POST[$field])) array_push($validation, $field);
    }
// basic validation result
if(count($validation) == 0) {
    // Prepare our content string
    $email_content = 'New Website Comment: ' . "'n'n";
    // simple email content
    foreach($_POST as $key => $value) {
        if($key != 'submit') $email_content .= $key . ': ' . $value . "'n";
    }
    // if validation passed ok then send the email
    mail($email_to, $email_subject, $email_content);
    // Update form switch
    $form_complete = TRUE;
}
}
function validate_email_address($email = FALSE) {
return (preg_match('/^[^@'s]+@([-a-z0-9]+'.)+[a-z]{2,}$/i', $email))? TRUE : FALSE;
}
function remove_email_injection($field = FALSE) {
   return (str_ireplace(array("'r", "'n", "%0a", "%0d", "Content-Type:", "bcc:","to:","cc:"), '', $field));
}
?>
<script type="text/javascript">
    var nameError = '<?php echo $error_messages['fullname']; ?>';
    var emailError = '<?php echo $error_messages['email']; ?>';
    var commentError = '<?php echo $error_messages['comment']; ?>';
</script>
</head>
<div id="formWrap">
<div id="form">
<?php if($form_complete === FALSE): ?>
<form action="/contact.php" method="post" id="comments_form">
    <div class="row">
    <div class="label">Name</div>
    <div class="input">
    <input type="text" id="fullname" class="detail" name="fullname" value="<?php echo isset($_POST['fullname'])? $_POST['fullname'] : ''; ?>" /><?php if(in_array('fullname', $validation)): ?><span class="error"><?php echo $error_messages['fullname']; ?></span><?php endif; ?>
    </div>
    <div class="context"></div>
    <div class="row">
    <div class="label">Your E-mail</div>
    <div class="input"><input type="text" id="email" class="detail" name="email" value="
<?php echo isset($_POST['email'])? $_POST['email'] : ''; ?>" />
<?php if(in_array('email', $validation)): ?><span class="error"><?php echo $error_messages['email']; ?></span><?php endif; ?>
    </div>
    <div class="context"></div>
    <div class="row">
    <div class="label">Select Physician</div>
    <div class="input"><select name='dropdown' >
<option value=''>
    --Select--</option>
<option value='phys1'>
    phys1</option>
<option value='phys2'>
    phys2</option>
<option value='phys3'>
    phys3</option>
</select>       </div>
    <div class="context"></div>

    <div class="row">
    <div class="label">
     Your Message</div>
    <div class="input">
    <textarea id="comment" name="comment" class="mess"><?php echo isset($_POST['comment'])? $_POST['comment'] : ''; ?></textarea><?php if(in_array('comment', $validation)): ?><span class="error"><?php echo $error_messages['comment']; ?></span><?php endif; ?>
    </div>
    </div>  
    <div class="submit"></div>
    <input type="submit" id="submit" name="submit" value="Send Message" />
</div>
</form>
<?php else: ?>
<p>
    Thank you for your message!</p>
 <?php endif; ?>
</div>
</div>
</div>
</div>
</div>
</div>  
</div>  
</body>
</html>

表格上传于此处：http://endotest.zxq.net/contact_test.php