diff --git a/django/core/mail.py b/django/core/mail.py
index d6c6eea190..1ac2a39908 100644
--- a/django/core/mail.py
+++ b/django/core/mail.py
@@ -86,6 +86,9 @@ def forbid_multi_line_headers(name, val):
             val = ', '.join(result)
         else:
             val = Header(val, settings.DEFAULT_CHARSET)
+    else:
+        if name.lower() == 'subject':
+            val = Header(val)
     return name, val
 
 class SafeMIMEText(MIMEText):
diff --git a/tests/regressiontests/mail/tests.py b/tests/regressiontests/mail/tests.py
index be59234342..ba08929137 100644
--- a/tests/regressiontests/mail/tests.py
+++ b/tests/regressiontests/mail/tests.py
@@ -10,6 +10,8 @@ r"""
 >>> email = EmailMessage('Subject', 'Content', 'from@example.com', ['to@example.com'])
 >>> message = email.message()
 >>> message['Subject']
+<email.header.Header instance...>
+>>> message['Subject'].encode()
 'Subject'
 >>> message.get_payload()
 'Content'
@@ -23,6 +25,8 @@ r"""
 >>> email = EmailMessage('Subject', 'Content', 'from@example.com', ['to@example.com','other@example.com'])
 >>> message = email.message()
 >>> message['Subject']
+<email.header.Header instance...>
+>>> message['Subject'].encode()
 'Subject'
 >>> message.get_payload()
 'Content'
@@ -45,4 +49,11 @@ Traceback (most recent call last):
     ...
 BadHeaderError: Header values can't contain newlines (got u'Subject\nInjection Test' for header 'Subject')
 
+# Test for space continuation character in long (ascii) subject headers (#7747)
+
+>>> email = EmailMessage('Long subject lines that get wrapped should use a space continuation character to get expected behaviour in Outlook and Thunderbird', 'Content', 'from@example.com', ['to@example.com'])
+>>> message = email.message()
+>>> message.as_string()
+'Content-Type: text/plain; charset="utf-8"\nMIME-Version: 1.0\nContent-Transfer-Encoding: quoted-printable\nSubject: Long subject lines that get wrapped should use a space continuation\n character to get expected behaviour in Outlook and Thunderbird\nFrom: from@example.com\nTo: to@example.com\nDate: ...\nMessage-ID: <...>\n\nContent'
+
 """