python
diff --git a/‎Lib/email/_header_value_parser.py
Copy file name to clipboardExpand all lines: Lib/email/_header_value_parser.py
+3-1Lines changed: 3 additions & 1 deletion b/‎Lib/email/_header_value_parser.py
Copy file name to clipboardExpand all lines: Lib/email/_header_value_parser.py
+3-1Lines changed: 3 additions & 1 deletion
diff --git a/‎Lib/test/test_email/test_generator.py
Copy file name to clipboardExpand all lines: Lib/test/test_email/test_generator.py
+32Lines changed: 32 additions & 0 deletions b/‎Lib/test/test_email/test_generator.py
Copy file name to clipboardExpand all lines: Lib/test/test_email/test_generator.py
+32Lines changed: 32 additions & 0 deletions
@@ -497,8 +497,10 @@ class Domain(TokenList):
 
     @property
     def domain(self):
-        return ''.join(super().value.split())
+        return ''.join(super().value.split()).encode('idna').decode('ascii')
 
+    def __str__(self):
+        return super().__str__().encode('idna').decode('ascii')
 
 class DotAtom(TokenList):
     token_type = 'dot-atom'
 
@@ -271,6 +271,38 @@ def test_cte_type_7bit_transforms_8bit_cte(self):
         g.flatten(msg)
         self.assertEqual(s.getvalue(), expected)
 
+    def test_unicode_domain_transforms_idna(self):
+        msg = EmailMessage()
+        msg['From'] = "john@examplé.com"
+        msg['To'] = "Joe <joe@examplé.com>"
+
+        expected = textwrap.dedent("""\
+            From: john@xn--exampl-gva.com
+            To: Joe <joe@xn--exampl-gva.com>
+
+            """).encode('ascii').replace(b'\n', b'\r\n')
+
+        s = io.BytesIO()
+        g = BytesGenerator(s, policy=policy.SMTP)
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), expected)
+
+    def test_unicode_domain_transforms_idna_smtputf8_policy(self):
+        msg = EmailMessage()
+        msg['From'] = "john@examplé.com"
+        msg['To'] = "Joe <joe@examplé.com>"
+
+        expected = textwrap.dedent("""\
+            From: john@xn--exampl-gva.com
+            To: Joe <joe@xn--exampl-gva.com>
+
+            """).encode('utf-8').replace(b'\n', b'\r\n')
+
+        s = io.BytesIO()
+        g = BytesGenerator(s, policy=policy.SMTPUTF8)
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), expected)
+
     def test_smtputf8_policy(self):
         msg = EmailMessage()
         msg['From'] = "Páolo <főo@bar.com>"