如何指定PHP应该使用外部邮件服务器发送mail()？

SMTP = "your.smtp.server"
smtp_port = 25
sendmail_from = "your@email.com"
sendmail_path = "path/to/sendmail"

<?php
require 'path/to/PHPMailer/src/Exception.php';
require 'path/to/PHPMailer/src/PHPMailer.php';
require 'path/to/PHPMailer/src/SMTP.php';

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$mail = new PHPMailer(true);

try {
    $mail->SMTPDebug = 2;
    $mail->isSMTP();
    $mail->Host = 'your.smtp.server';
    $mail->SMTPAuth = true;
    $mail->Username = 'your@email.com';
    $mail->Password = 'your_password';
    $mail->SMTPSecure = 'tls';
    $mail->Port = 587;

    $mail->setFrom('your@email.com', 'Your Name');
    $mail->addAddress('recipient@example.com', 'Recipient Name');

    $mail->isHTML(true);
    $mail->Subject = 'Subject';
    $mail->Body = 'This is the HTML message body <b>in bold!</b>';
    $mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

    $mail->send();
    echo 'Message has been sent';
} catch (Exception $e) {
    echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}

<?php
$url = 'https://your.smtp.server/sendmail';
$data = array(
    'from' => 'your@email.com',
    'to' => 'recipient@example.com',
    'subject' => 'Subject',
    'text' => 'This is the message body',
    'api_key' => 'your_api_key'
);

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($data));
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
curl_close($ch);

echo $response;