diff --git a/django/core/mail/message.py b/django/core/mail/message.py
index a0cb09f7b8..2311102fd0 100644
--- a/django/core/mail/message.py
+++ b/django/core/mail/message.py
@@ -67,7 +67,11 @@ def forbid_multi_line_headers(name, val, encoding):
             result = []
             for nm, addr in getaddresses((val,)):
                 nm = str(Header(nm.encode(encoding), encoding))
-                result.append(formataddr((nm, str(addr))))
+                try:
+                    addr = addr.encode('ascii')
+                except UnicodeEncodeError:  # IDN
+                    addr = str(Header(addr.encode(encoding), encoding))
+                result.append(formataddr((nm, addr)))
             val = ', '.join(result)
         else:
             val = Header(val.encode(encoding), encoding)
diff --git a/tests/regressiontests/mail/tests.py b/tests/regressiontests/mail/tests.py
index d2f7562d8f..a84417e21b 100644
--- a/tests/regressiontests/mail/tests.py
+++ b/tests/regressiontests/mail/tests.py
@@ -363,3 +363,18 @@ class MailTests(TestCase):
 
         settings.ADMINS = old_admins
         settings.MANAGERS = old_managers
+
+    def test_idn_validation(self):
+        """Test internationalized email adresses"""
+        # Regression for #14301.
+        mail.outbox = []
+        from_email = u'fröm@öäü.com'
+        to_email = u'tö@öäü.com'
+        connection = mail.get_connection('django.core.mail.backends.locmem.EmailBackend')
+        send_mail('Subject', 'Content', from_email, [to_email], connection=connection)
+        self.assertEqual(len(mail.outbox), 1)
+        message = mail.outbox[0]
+        self.assertEqual(message.subject, 'Subject')
+        self.assertEqual(message.from_email, from_email)
+        self.assertEqual(message.to, [to_email])
+        self.assertTrue(message.message().as_string().startswith('Content-Type: text/plain; charset="utf-8"\nMIME-Version: 1.0\nContent-Transfer-Encoding: quoted-printable\nSubject: Subject\nFrom: =?utf-8?b?ZnLDtm1Aw7bDpMO8LmNvbQ==?=\nTo: =?utf-8?b?dMO2QMO2w6TDvC5jb20=?='))