如何使用谷歌应用引擎使用自定义域(https）的Sendgrid发送电子邮件

我有一个在谷歌应用引擎上托管的web应用程序，它是用Codeigner（PHP）编写的。我使用sendgrid发送事务性电子邮件。

该应用最初托管在https://appid.appspot.com一切都很好。

我最近将应用程序URL更改为https://app.domain.com并导入了我从godaddy购买的SSL证书。就ssl证书而言，我没有任何问题。

然而，在发送事务性电子邮件时，我收到了以下错误。

Severity: Warning
Message: fsockopen(): php_network_getaddresses: gethostbyname failed. errno=0
Filename: libraries/Email.php
Line Number: 1949
Backtrace:
File: /base/data/home/apps/s~chutti-app-prod/1.388253899009796980/application/controllers/Signup.php
Line: 60
Function: send
File: /base/data/home/apps/s~chutti-app-prod/1.388253899009796980/index.php
Line: 292
Function: require_once
A PHP Error was encountered
Severity: Warning
Message: fsockopen(): unable to connect to smtp.sendgrid.net:587 (php_network_getaddresses: gethostbyname failed. errno=0)
Filename: libraries/Email.php
Line Number: 1949
Backtrace:
File: /base/data/home/apps/s~chutti-app-prod/1.388254166863409817/application/controllers/Signup.php
Line: 60
Function: send
File: /base/data/home/apps/s~chutti-app-prod/1.388254166863409817/index.php
Line: 292
Function: require_once

sendgrid凭据与我在托管于的不同应用程序中使用的凭据相同https://app.appspot.com一切都很好。问题只出在我使用https的自定义URL上。

发送电子邮件的代码

$this->load->library('email');
$this->email->initialize(array(
              'protocol' => 'smtp',
              'smtp_host' => 'smtp.sendgrid.net',
              'smtp_user' => 'username',
              'smtp_pass' => 'password',
              'smtp_port' => 587,
              'crlf' => "'r'n",
              'newline' => "'r'n"
        ));

        $body = 'some html content';
        $this->email->set_mailtype("html");
        $this->email->from('noreply@domain.com');
        $this->email->to('to@userdomain.com');
        $this->email->subject('Please confirm your email');
        $this->email->message($body);
        $this->email->send();

如果有人能帮我弄清楚问题到底是什么，那就太好了。