🐛 修复邮件发送功能的小问题

- 修复发件人字段处理，避免空字符串导致发送失败
- 改进SMTP测试错误消息显示，支持详细错误信息
- 更新package-lock.json锁定nodemailer版本

这些修复提升了邮件功能的稳定性和错误提示的友好性。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/package-lock.json

@@ -21,6 +21,7 @@
         "express-validator": "^7.3.0",
         "jsonwebtoken": "^9.0.2",
         "multer": "^2.0.2",
+        "nodemailer": "^6.9.14",
         "ssh2-sftp-client": "^12.0.1",
         "svg-captcha": "^1.4.0"
       },
@@ -1913,6 +1914,15 @@
         "node": ">=10"
       }
     },
+    "node_modules/nodemailer": {
+      "version": "6.10.1",
+      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-6.10.1.tgz",
+      "integrity": "sha512-Z+iLaBGVaSjbIzQ4pX6XV41HrooLsQ10ZWPUehGmuantvzWoDVBnmsdUcOIDM1t+yPor5pDhVlDESgOMEGxhHA==",
+      "license": "MIT-0",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/nodemon": {
       "version": "3.1.10",
       "resolved": "https://registry.npmjs.org/nodemon/-/nodemon-3.1.10.tgz",

backend/server.js

@@ -695,8 +695,10 @@ async function sendMail(to, subject, html) {
     throw new Error('SMTP未配置');
   }
 
+  const from = (config.from && config.from.trim()) ? config.from.trim() : config.auth.user;
+
   await transporter.sendMail({
-    from: config.from,
+    from,
     to,
     subject,
     html
@@ -2879,7 +2881,7 @@ app.post('/api/admin/settings/test-smtp', authMiddleware, adminMiddleware, async
     res.json({ success: true, message: `测试邮件已发送至 ${target}` });
   } catch (error) {
     console.error('测试SMTP失败:', error);
-    res.status(500).json({ success: false, message: '测试邮件发送失败: ' + error.message });
+    res.status(500).json({ success: false, message: '测试邮件发送失败: ' + (error.response?.message || error.message) });
   }
 });