针对ME
的固定问题我通过下载更新后的根证书文件并将我的php.ini文件指向它来解决了我在windows php环境中的这个问题。
似乎问题不在于使用gmail的证书，而是由于windows server 2012不再自动更新该文件，而是使用了过期的根证书文件。从这里下载cacert.pem： https://curl.haxx.se/docs/caextract.html 。然后在php.ini中使用以下行指向它（假设你已经安装了openssl.dll）。

openssl.cafile = {服务器上的文件路径} \cacert.pem。

解决了这个问题，我不再需要像建议的那样绕过SSL / TLS验证。最终，我需要让Windows使用GPO或WSUS自动更新根证书。请参阅 https：/ /serverfault.com/questions/541922/where-to-get-root-ca-certificates-for-windows-server-now-that-microsoft-no-longe

Very recently encountered this error when trying to send mail via SMTP and GMail.

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:

Server address is https://gg-portal.com, and SSL configuration seems correct (verified through online checkers).

PHPMailer code is...

$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;
}

Have looked at the documentation which suggests certificate issues, though as stated SSL setup seems fine. Have looked into the issue elsewhere and most popular suggestions is to bypass the SSL (which works) however I'd prefer not to do this.

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

FIXED ISSUE FOR ME I fixed this issue in my windows php environment by downloading an updated root certificates file and pointing my php.ini file to it. It seems the problem was not with gmail's cert but rather with an outdated root certificate file due to windows server 2012 no longer updating this file automatically. Download cacert.pem from here: https://curl.haxx.se/docs/caextract.html. Then in php.ini use following line to point to it (assuming you have openssl.dll installed).

openssl.cafile={Path to the file on your server}\cacert.pem.

That fixed it and I no longer needed to bypass SSL/TLS verification like suggested. Ultimately I need to get windows to update root certs automatically using GPO or WSUS. see https://serverfault.com/questions/541922/where-to-get-root-ca-certificates-for-windows-server-now-that-microsoft-no-longe