PHP를 통해 이메일 암호화 및 암호 해독 기능을 구현하는 방법은 무엇입니까?

<?php
// 加密邮件内容
function encryptMail($emailContent, $publicKeyFile) {
    $publicKey = openssl_pkey_get_public(file_get_contents($publicKeyFile));
    openssl_public_encrypt($emailContent, $encryptedContent, $publicKey);
    return base64_encode($encryptedContent);
}

// 发送加密邮件
function sendEncryptedMail($emailContent, $publicKeyFile, $recipient) {
    $encryptedContent = encryptMail($emailContent, $publicKeyFile);
    
    // 发送加密邮件，这里使用其他邮件发送方法进行发送
    // ...
    // 发送加密邮件的代码
    // ...
}

// 测试
$emailContent = "Hello, this is a test email.";
$publicKeyFile = "public_key.pem";
$recipient = "recipient@example.com";
sendEncryptedMail($emailContent, $publicKeyFile, $recipient);
?>

<?php
// 解密邮件内容
function decryptMail($encryptedContent, $privateKeyFile) {
    $privateKey = openssl_pkey_get_private(file_get_contents($privateKeyFile));
    openssl_private_decrypt(base64_decode($encryptedContent), $decryptedContent, $privateKey);
    return $decryptedContent;
}

// 接收解密邮件
function receiveDecryptedMail($encryptedContent, $privateKeyFile) {
    $decryptedContent = decryptMail($encryptedContent, $privateKeyFile);
    
    // 打印解密后的邮件内容
    echo $decryptedContent;
}

// 测试
$encryptedContent = "encrypted content";
$privateKeyFile = "private_key.pem";
receiveDecryptedMail($encryptedContent, $privateKeyFile);
?>