diff --git a/backend/utils/send/send.go b/backend/utils/send/send.go
index 0588cf9..222da49 100644
--- a/backend/utils/send/send.go
+++ b/backend/utils/send/send.go
@@ -270,7 +270,7 @@ func doSend(ctx *context.Context, fromDomain string, data []byte, to []*parsemai
 				}
 			}()
 
-			if domain == consts.TEST_DOMAIN {
+			if domain == consts.TEST_DOMAIN || isConfiguredMailDomain(domain, config.CurrentMailDomains().Accepted) {
 				err := smtp.SendMailUnsafeContext(deliveryContext, "localhost", "127.0.0.1:25", nil, from, fromDomain, buildAddress(tos), data)
 				if err != nil {
 					recordFailure(err)
@@ -336,6 +336,21 @@ func allowUnsafeSMTP(domain mxDomain) bool {
 	return domain.localTest && domain.domain == "localhost" && domain.mxHost == "127.0.0.1"
 }
 
+// isConfiguredMailDomain 判断收件域名是否属于当前 Smail 实例管理的域名。
+// 受管域名应交给本机 SMTP 服务处理，避免内部账户互发依赖公网 DNS 和 MX。
+func isConfiguredMailDomain(domain string, accepted []string) bool {
+	domain = strings.ToLower(strings.TrimSpace(domain))
+	if domain == "" {
+		return false
+	}
+	for _, item := range accepted {
+		if domain == strings.ToLower(strings.TrimSpace(item)) {
+			return true
+		}
+	}
+	return false
+}
+
 func isCertificateVerificationError(err error) bool {
 	var certificateErr *tls.CertificateVerificationError
 	return errors.As(err, &certificateErr)
diff --git a/backend/utils/send/send_test.go b/backend/utils/send/send_test.go
index e750fb2..415f7cb 100644
--- a/backend/utils/send/send_test.go
+++ b/backend/utils/send/send_test.go
@@ -113,6 +113,28 @@ func TestAllowUnsafeSMTPRequiresExplicitLoopbackTestTarget(t *testing.T) {
 	}
 }
 
+func TestIsConfiguredMailDomain(t *testing.T) {
+	accepted := []string{"cdis.cn", "alias.cdis.cn"}
+	tests := []struct {
+		name   string
+		domain string
+		want   bool
+	}{
+		{name: "primary domain", domain: "cdis.cn", want: true},
+		{name: "case insensitive domain", domain: "CDIS.CN", want: true},
+		{name: "accepted alias", domain: "alias.cdis.cn", want: true},
+		{name: "external domain", domain: "example.com"},
+		{name: "empty domain"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isConfiguredMailDomain(tt.domain, accepted); got != tt.want {
+				t.Fatalf("isConfiguredMailDomain(%q) = %v, want %v", tt.domain, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestParseRecipientAddressRejectsUnsafeInput(t *testing.T) {
 	tests := []struct {
 		name string