'Swift_TransportException'，带有消息'预期响应代码220但得到代码“”

Question

我有一个通过SMTP发送邮件的代码

if (isset ($_POST['Message'])) {
    $message = $_POST['url']."
    :".$_POST["Message"];
    $message0 = wordwrap($message, 70, "\r\n");
    \Yii::$app->mailer->useFileTransport=false;
    \Yii::$app->mailer->setTransport([
        'class' => 'Swift_SmtpTransport',
        'host' => 'mail.myhost.com',
        'username' => 'info@myhost.com',
        'password' => 'pass',
        'port' => '25',
    ]);
    $message = \Yii::$app->mailer->compose();
    $contentEncoder7bit = new \Swift_Mime_ContentEncoder_PlainContentEncoder('7bit');
    $message->getSwiftMessage()->setEncoder($contentEncoder7bit);
    \Swift_MimePart::newInstance();
    $message->setFrom('info@myhost.com')
        ->setTo('korrektor@mail.com')
        ->setSubject('Sunbject')
        ->setTextBody($message0);
    $message->send();
    return;
}

在发送邮件时，我收到错误

exception 'Swift_TransportException' with message 'Expected response code 220 but got code "", with message ""'  in
C:\wamp\www\yii\vendor\swiftmailer\swiftmailer\lib\classes\Swift\Transport\AbstractSmtpTransport.php:383
Stack trace: 
#0 C:\wamp\www\yii\vendor\swiftmailer\swiftmailer\lib\classes\Swift\Transport\AbstractSmtpTransport.php(289):
Swift_Transport_AbstractSmtpTransport->_assertResponseCode('', Array) 
#1 C:\wamp\www\yii\vendor\swiftmailer\swiftmailer\lib\classes\Swift\Transport\AbstractSmtpTransport.php(117):
Swift_Transport_AbstractSmtpTransport->_readGreeting() 
#2 C:\wamp\www\yii\vendor\swiftmailer\swiftmailer\lib\classes\Swift\Mailer.php(79):
Swift_Transport_AbstractSmtpTransport->start() 
#3 C:\wamp\www\yii\vendor\yiisoft\yii2-swiftmailer\Mailer.php(146): Swift_Mailer->send(Object(Swift_Message)) 
#4 C:\wamp\www\yii\vendor\yiisoft\yii2\mail\BaseMailer.php(262): yii\swiftmailer\Mailer->sendMessage(Object(yii\swiftmailer\Message)) 
#5 C:\wamp\www\yii\vendor\yiisoft\yii2\mail\BaseMessage.php(48): yii\mail\BaseMailer->send(Object(yii\swiftmailer\Message)) 
#6 C:\wamp\www\yii\frontend\controllers\SiteController.php(1982): yii\mail\BaseMessage->send() 
#7 [internal function]: frontend\controllers\SiteController->actionSendorphus() 
#8 C:\wamp\www\yii\vendor\yiisoft\yii2\base\InlineAction.php(57): call_user_func_array(Array, Array) 
#9 C:\wamp\www\yii\vendor\yiisoft\yii2\base\Controller.php(156): yii\base\InlineAction->runWithParams(Array) 
#10 C:\wamp\www\yii\vendor\yiisoft\yii2\base\Module.php(523): yii\base\Controller->runAction('sendorphus', Array) 
#11 C:\wamp\www\yii\vendor\yiisoft\yii2\web\Application.php(102): yii\base\Module->runAction('site/sendorphus', Array) 
#12 C:\wamp\www\yii\vendor\yiisoft\yii2\base\Application.php(380): yii\web\Application->handleRequest(Object(yii\web\Request)) 
#13 C:\wamp\www\yii\frontend\web\index.php(19): yii\base\Application->run() 
#14 {main}