feat: Implement core backend API server with configuration, S2A proxy, and mail service APIs, and introduce EmailConfig frontend page.

backend/cmd/main.go

@@ -344,16 +344,19 @@ func handleMailServices(w http.ResponseWriter, r *http.Request) {
 	switch r.Method {
 	case "GET":
 		services := mail.GetServices()
-		safeServices := make([]map[string]interface{}, len(services))
+		// 返回完整配置（包括 token）供前端加载
+		result := make([]map[string]interface{}, len(services))
 		for i, s := range services {
-			safeServices[i] = map[string]interface{}{
-				"name":      s.Name,
-				"api_base":  s.APIBase,
-				"has_token": s.APIToken != "",
-				"domain":    s.Domain,
+			result[i] = map[string]interface{}{
+				"name":       s.Name,
+				"apiBase":    s.APIBase,
+				"apiToken":   s.APIToken,
+				"domain":     s.Domain,
+				"emailPath":  s.EmailPath,
+				"addUserApi": s.AddUserAPI,
 			}
 		}
-		api.Success(w, safeServices)
+		api.Success(w, result)
 	case "POST":
 		var req struct {
 			Services []struct {
@@ -393,7 +396,7 @@ func handleMailServices(w http.ResponseWriter, r *http.Request) {
 			})
 		}
 
-		// 更新邮箱服务配置
+		// 更新邮箱服务配置（内存）
 		mail.Init(services)
 
 		// 保存到全局配置
@@ -401,6 +404,14 @@ func handleMailServices(w http.ResponseWriter, r *http.Request) {
 			config.Global.MailServices = services
 		}
 
+		// 持久化到数据库
+		if database.Instance != nil {
+			jsonData, _ := json.Marshal(services)
+			if err := database.Instance.SetConfig("mail_services", string(jsonData)); err != nil {
+				logger.Error(fmt.Sprintf("保存邮箱配置到数据库失败: %v", err), "", "mail")
+			}
+		}
+
 		logger.Success(fmt.Sprintf("邮箱服务配置已保存: %d 个服务", len(services)), "", "mail")
 		for _, s := range services {
 			logger.Info(fmt.Sprintf("  - %s (%s) @ %s", s.Name, s.Domain, s.APIBase), "", "mail")
@@ -483,8 +494,15 @@ func handleTestMailService(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// 判断结果
-	if result.Code == 200 || strings.Contains(result.Message, "exist") {
-		logger.Success(fmt.Sprintf("邮箱服务测试成功: %s", req.Name), "", "mail")
+	// code 200 = 创建成功
+	// code 501 且消息包含"已存在" = 邮箱已存在，说明连接正常
+	isSuccess := result.Code == 200 ||
+		strings.Contains(result.Message, "exist") ||
+		strings.Contains(result.Message, "已存在") ||
+		(result.Code == 501 && strings.Contains(result.Message, "邮箱"))
+
+	if isSuccess {
+		logger.Success(fmt.Sprintf("邮箱服务测试成功: %s (邮箱已存在或创建成功)", req.Name), "", "mail")
 		api.Success(w, map[string]interface{}{
 			"connected": true,
 			"message":   "邮箱服务连接成功",