发送电子邮件时通过需要SMTP认证的服务器，您真的需要指定它，并设置主机，用户名和密码（也可能是端口，如果不是默认端口）。

When you are sending an e-mail through a server that requires SMTP Auth, you really need to specify it, and set the host, username and password (and maybe the port if it is not the default one - 25).

例如，我通常使用PHPMailer与此类似的设置：

For example, I usually use PHPMailer with similar settings to this ones:

$mail = new PHPMailer();
$mail->IsSMTP();
$mail->CharSet = 'UTF-8';

$mail->Host       = "mail.example.com"; // SMTP server example
$mail->SMTPDebug  = 0;                     // enables SMTP debug information (for testing)
$mail->SMTPAuth   = true;                  // enable SMTP authentication
$mail->Port       = 25;                    // set the SMTP port for the GMAIL server
$mail->Username   = "username"; // SMTP account username example
$mail->Password   = "password";        // SMTP account password example

您可以在这里找到有关PHPMailer的更多信息： https://github.com/PHPMailer/PHPMailer

You can find more about PHPMailer here: https://github.com/PHPMailer/PHPMailer