如何为现有PHP邮件表单添加附件功能并限制文件大小？

先修正你的HTML表单——原代码里嵌套了<form>标签，这会导致上传失效，而且文件上传必须加enctype="multipart/form-data"才能正确传递文件。修改后的HTML如下：

<form id="booking-form" class="booking-form" name="form1" method="post" action="" enctype="multipart/form-data">
    <div align="center"><img class="logo" src="img/example_logo.png" title="Example Logo" alt="Example Logo"></div>
    <div class="h1"><strong>Kontaktieren Sie uns</strong></div>
    <div id="form-message" class="message hide">
        Vielen Dank für Ihre Anfrage, wir werden uns so schnell wie möglich bei Ihnen melden, um Ihre Anfrage zu bearbeiten<br><a class="" href="../index.html">zurück zur Homepage</a>
    </div>
    <div id="form-content">
        <div class="group">
            <label for="name">Name:</label>
            <div><input id="name" name="name" class="form-control" type="text" placeholder=""></div>
        </div>
        <div class="group">
            <label for="email">Email:</label>
            <div><input id="email" name="email" class="form-control" type="email" placeholder=""></div>
        </div>
        <div class="group">
            <label for="phone">Telefon:</label>
            <div><input id="phone" name="phone" class="form-control" type="number" placeholder=""></div>
        </div>
        <div class="group">
            <label for="special-requirements">Nachricht:</label>
            <div><textarea id="special-requirements" name="special-requirements" class="form-control" cols="" rows="5" placeholder=""></textarea></div>
        </div>
        <div class="group">
            <label for="myFile">附件:</label>
            <div><input type="file" id="myFile" name="filename"></div>
        </div>
        <div class="group">
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<input type="radio" name="AGB" value="OK" checked>Hiermit akzeptiere ich die <a href="../DSGVO.html">DSGVO</a>
        </div>
        <div class="group submit">
            <label class="empty"></label>
            <div><input name="submit" type="submit" value="Absenden"/></div>
        </div>
    </div>
    <div id="form-loading" class="hide"><i class="fa fa-circle-o-notch fa-spin"></i></div>
</form>

HTML修改要点：

• 删除了嵌套的多余<form>标签
• 主表单添加enctype="multipart/form-data"属性（文件上传必备）
• 给文件按钮补充了标签，优化界面可读性

接下来修改PHP脚本，实现文件大小限制和带附件的邮件发送：

<?php
define('_EMAIL_TO', 'xxx@xxx.xx'); // 收件邮箱地址
define('_EMAIL_SUBJECT', 'XXX'); // 邮件主题
define('_MAX_FILE_SIZE', 5 * 1024 * 1024); // 5MB大小限制，单位字节

$error_fields = array();
$email_content = array();

// 表单字段验证逻辑
$fields = array(
    array('name' => 'AGB', 'title' => 'AGB '),
    array('name' => 'name', 'title' => 'Name', 'valid' => array('require')),
    array('name' => 'phone', 'title' => 'Telefon', 'valid' => array('require')),
    array('name' => 'email', 'title' => 'Email', 'valid' => array('require', 'email')),
    array('name' => 'special-requirements', 'title' => 'Nachricht')
);

foreach ($fields AS $field){
    $value = isset($_POST[$field['name']])?$_POST[$field['name']]:'';
    $title = empty($field['title'])?$field['name']:$field['title'];
    $email_content[] = $title.': '.nl2br(stripslashes($value));
    $is_valid = true;
    $err_message = '';
    if (!empty($field['valid'])){
        foreach ($field['valid'] AS $valid) {
            switch ($valid) {
                case 'require':
                    $is_valid = $is_valid && strlen($value) > 0;
                    $err_message = '此字段为必填项';
                    break;
                case 'email':
                    $is_valid = $is_valid && preg_match("/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$/i", $value);
                    $err_message = '请输入有效的邮箱地址';
                    break;
                default:                
                    break;
            }
        }
    }
    if (!$is_valid){
        if (!empty($field['err_message'])){
            $err_message = $field['err_message'];
        }
        $error_fields[] = array('name' => $field['name'], 'message' => $err_message);
    }
}

// 处理文件上传验证
$attachment = null;
if (!empty($_FILES['filename']['name'])) {
    // 检查文件大小是否超标
    if ($_FILES['filename']['size'] > _MAX_FILE_SIZE) {
        $error_fields[] = array('name' => 'filename', 'message' => '附件大小不能超过5MB');
    }
    // 检查上传是否出错
    if ($_FILES['filename']['error'] !== UPLOAD_ERR_OK) {
        $error_fields[] = array('name' => 'filename', 'message' => '文件上传失败，请重试');
    }
    // 读取文件内容（验证通过后）
    if (empty($error_fields)) {
        $attachment = array(
            'name' => $_FILES['filename']['name'],
            'type' => $_FILES['filename']['type'],
            'content' => file_get_contents($_FILES['filename']['tmp_name'])
        );
    }
}

// 发送邮件
if (empty($error_fields)) {
    $from_email = $_POST['email'];
    $boundary = uniqid('np'); // 生成唯一的邮件内容分隔符

    // 构建邮件头部
    $headers = "MIME-Version: 1.0\r\n";
    $headers .= "From: $from_email\r\n";
    $headers .= "Reply-To: $from_email\r\n";
    $headers .= "Content-Type: multipart/mixed; boundary=" . $boundary . "\r\n";

    // 邮件正文内容
    $message = "--" . $boundary . "\r\n";
    $message .= "Content-Type: text/html; charset=utf-8\r\n";
    $message .= "Content-Transfer-Encoding: 8bit\r\n\r\n";
    $message .= implode('<hr>', $email_content) . "\r\n\r\n";

    // 添加附件（如果有）
    if ($attachment) {
        $message .= "--" . $boundary . "\r\n";
        $message .= "Content-Type: " . $attachment['type'] . "; name=\"" . $attachment['name'] . "\"\r\n";
        $message .= "Content-Transfer-Encoding: base64\r\n";
        $message .= "Content-Disposition: attachment; filename=\"" . $attachment['name'] . "\"\r\n\r\n";
        $message .= chunk_split(base64_encode($attachment['content'])) . "\r\n";
    }

    // 结束分隔符
    $message .= "--" . $boundary . "--";

    // 发送邮件并返回结果
    if (mail(_EMAIL_TO, _EMAIL_SUBJECT, $message, $headers)) {
        echo json_encode(array('code' => 'success'));
    } else {
        $error_fields[] = array('name' => 'system', 'message' => '邮件发送失败，请稍后重试');
        echo json_encode(array('code' => 'failed', 'fields' => $error_fields));
    }
} else {
    echo json_encode(array('code' => 'failed', 'fields' => $error_fields));
}
?>

PHP修改要点：

1. 新增_MAX_FILE_SIZE常量，明确设置5MB的文件大小限制
2. 加入文件上传验证逻辑：检查文件大小、上传错误状态
3. 重构邮件结构，使用multipart/mixed MIME类型实现附件支持
4. 将附件内容转成Base64编码，符合邮件传输规范
5. 完善错误处理，新增邮件发送失败的反馈

额外提醒： #

• 确保PHP配置中的upload_max_filesize和post_max_size参数值不小于5MB（可在php.ini中修改，或用ini_set()临时调整）
• 如果需要限制文件类型，可以在文件验证部分添加扩展名或MIME类型检查
• 上传的临时文件会在脚本执行完毕后自动删除，无需手动清理

内容的提问来源于stack exchange，提问作者Johannes Pohle