无法连接到GMail SMTP(PHPMailer)-证书验证失败

最近在尝试通过SMTP和GMail发送邮件时遇到此错误。

Warning: stream_socket_enable_crypto(): SSL operation failed with code 1.
OpenSSL Error messages: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed in C:\xampp\htdocs\portal\libraries\php_mailer\class.smtp.php on line 343
2017-12-05 09:48:03 SMTP Error: Could not connect to SMTP host. 
2017-12-05 09:48:03 CLIENT -> SERVER: QUIT 
2017-12-05 09:48:03 SMTP ERROR: QUIT command failed:

服务器地址为 https://gg-portal.com SSL配置似乎正确(通过在线检查验证)。

PHP编译器代码为。。。

$mail = new PHPMailer();
$mail->isSMTP();
$mail->Host = "smtp.gmail.com";
$mail->SMTPAuth = true;
$mail->Username = $this->_config["EmailUser"];
$mail->Password = $this->_config["EmailPass"];
$mail->SMTPSecure = "tls";
$mail->SMTPDebug = 1;
$mail->Port = 587;
$mail->FromName = $this->_config["Brand"];  
$mail->From     = $this->_config["EmailFrom"];
$mail->AddCC("...emailAddress...");
$mail->Subject  = "...subject...";
$mail->Body     = "...content...";
$mail->IsHTML(true);  
$mail->WordWrap = 50;
if(!$mail->Send()) {
    echo ' Message was not sent.';
    echo 'Mailer error: ' . $mail->ErrorInfo;
}

我们已经阅读了建议证书问题的文档,尽管如前所述,SSL设置似乎很好。我已经在其他地方研究了这个问题,最流行的建议是绕过SSL(它可以工作),但是我不愿意这样做。

'context' => [
    'ssl' => [
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
    ]
]