一个简单的电子邮件客户端/联系表单返回“5.5.4无效域错误”，我已经用尽所有资源试图解决它

Question

在过去的两天里，我已经两次发布了这个问题，而且我真的已经解决了这个问题。我创建了一个非常简单的评论框，填写后会在电子邮件中将评论发送给我公司的安全部门。我在过去几天收到了5.5.4无效域错误。

它的SMTP和TLS。端口和服务器名称是正确的。服务器允许匿名电子邮件，但不验证。我使用的是Swiftmailer库，因此我不需要编写ELHO / HELO脚本。电子邮件中唯一未定义/硬编码的属性是邮件正文。这是我的控制器的代码（index.php）。

// Initialize Swiftmailer Library
require_once("./swiftmailer/lib/swift_required.php"); 

// Class that contains the information of the email that will be sent (from, to, etc.)
require_once("./classes/EmailParts.php");

// The class that "breaks" the data sent with the HTML form to a more "usable" format.
require_once("./classes/ContactForm.php");

// =====================
// Main Configuration
// =====================

define("EMAIL_SUBJECT", "Safety Concerns");     
define("EMAIL_TO", "safetydepartment@company.com"); 
define("EMAIL_FROM", "safetydepartment@company.com");   

// SMTP Configuration
define("SMTP_SERVER", 'exchange.company.local');                
define("SMTP_PORT", 25);                                

function main($contactForm) {

    // Checks if something was sent to the contact form, if not, do nothing
    if (!$contactForm->isDataSent()) {
        return;
    }

    // Validates the contact form and checks for errors
    $contactForm->validate();

    $errors = array();

    // If the contact form is not valid:
    if (!$contactForm->isValid()) {
        // gets the error in the array $errors
        $errors = $contactForm->getErrors();

    } else {
        // If the contact form is valid:
        try {               
            // send the email created with the contact form
            $result = sendEmail($contactForm);              

            // after the email is sent, redirect and "die".
            // We redirect to prevent refreshing the page which would resend the form
            header("Location: ./success.php");
            die();
        } catch (Exception $e) {
            // an error occured while sending the email. 
            // Log the error and add an error message to display to the user.
            error_log('An error happened while sending email contact form: ' . $e->getMessage());
            $errors['oops'] = 'Ooops! an error occured while sending your email! Please try again later!';
        }

    }

    return $errors;
}

// Sends the email based on the information contained in the contact form
function sendEmail($contactForm) {
    // Email part will create the email information needed to send an email based on 
    // what was inserted inside the contact form
    $emailParts = new EmailParts($contactForm);

    // This is the part where we initialize Swiftmailer with 
    // all the info initialized by the EmailParts class
    $emailMessage = Swift_Message::newInstance()
    ->setSubject($emailParts->getSubject())
    ->setFrom($emailParts->getFrom())
    ->setTo($emailParts->getTo())
    ->setBody($emailParts->getBodyMessage());

    // Another Swiftmailer configuration..
    $transport = Swift_SmtpTransport::newInstance(SMTP_SERVER, SMTP_PORT, 'tls');
    $mailer = Swift_Mailer::newInstance($transport);
    $result = $mailer->send($emailMessage);
    return $result;
}

// Initialize the ContactForm with the information of the form and the possible uploaded file.
$contactForm = new ContactForm($_POST, $_FILES);

// Call the "main" method. It will return a list of errors. 
$errors = main($contactForm);

// Call the "contactForm" view to display the HTML contact form.
require_once("./views/contactForm.php");

我已在Dropbox发布了我的全部代码。虽然不多，但我认为问题必须在索引中。