diff --git a/flask_mailman/utils.py b/flask_mailman/utils.py
index d8ea9d8..a5f5b92 100644
--- a/flask_mailman/utils.py
+++ b/flask_mailman/utils.py
@@ -14,7 +14,7 @@ def __str__(self):
 
     def get_fqdn(self):
         if not hasattr(self, '_fqdn'):
-            self._fqdn = socket.getfqdn()
+            self._fqdn = punycode(socket.getfqdn())
         return self._fqdn
 
 
diff --git a/tests/test_mail.py b/tests/test_mail.py
index 7200add..5ef0c64 100644
--- a/tests/test_mail.py
+++ b/tests/test_mail.py
@@ -425,6 +425,13 @@ def test_none_body(self):
         self.assertEqual(msg.body, "")
         self.assertEqual(msg.message().get_payload(), "")
 
+    @mock.patch("socket.getfqdn", return_value="漢字")
+    def test_non_ascii_dns_non_unicode_email(self, mocked_getfqdn):
+        delattr(DNS_NAME, "_fqdn")
+        email = EmailMessage("subject", "content", "from@example.com", ["to@example.com"])
+        email.encoding = "iso-8859-1"
+        self.assertIn("@xn--p8s937b>", email.message()["Message-ID"])
+
     def test_encoding(self):
         """
         Regression for #12791 - Encode body correctly with other encodings