diff --git a/Doc/library/email.errors.rst b/Doc/library/email.errors.rst
index d8f330f4bec..b71ffa041c0 100644
--- a/Doc/library/email.errors.rst
+++ b/Doc/library/email.errors.rst
@@ -79,9 +79,18 @@ this class is *not* an exception!
 * :class:`MisplacedEnvelopeHeaderDefect` - A "Unix From" header was found in the
   middle of a header block.
 
+* :class:`MissingHeaderBodySeparatorDefect` - A line was found while parsing
+  headers that had no leading white space but contained no ':'.  Parsing
+  continues assuming that the line represents the first line of the body.
+
+  .. versionadded: 3.3
+
 * :class:`MalformedHeaderDefect` -- A header was found that was missing a colon,
   or was otherwise malformed.
 
+  .. deprecated:: 3.3
+     This defect has not been used for several Python versions.
+
 * :class:`MultipartInvariantViolationDefect` -- A message claimed to be a
   :mimetype:`multipart`, but no subparts were found.  Note that when a message has
   this defect, its :meth:`is_multipart` method may return false even though its
diff --git a/Lib/email/errors.py b/Lib/email/errors.py
index f9162292f9c..aa836d49c77 100644
--- a/Lib/email/errors.py
+++ b/Lib/email/errors.py
@@ -48,8 +48,10 @@ class FirstHeaderLineIsContinuationDefect(MessageDefect):
 class MisplacedEnvelopeHeaderDefect(MessageDefect):
     """A 'Unix-from' header was found in the middle of a header block."""
 
-class MalformedHeaderDefect(MessageDefect):
-    """Found a header that was missing a colon, or was otherwise malformed."""
+class MissingHeaderBodySeparatorDefect(MessageDefect):
+    """Found line with no leading whitespace and no colon before blank line."""
+# XXX: backward compatibility, just in case (it was never emitted).
+MalformedHeaderDefect = MissingHeaderBodySeparatorDefect
 
 class MultipartInvariantViolationDefect(MessageDefect):
     """A message claimed to be a multipart but no subparts were found."""
diff --git a/Lib/email/feedparser.py b/Lib/email/feedparser.py
index 0706cae9bf9..c3a67c0927e 100644
--- a/Lib/email/feedparser.py
+++ b/Lib/email/feedparser.py
@@ -219,6 +219,8 @@ class FeedParser:
                 # (i.e. newline), just throw it away. Otherwise the line is
                 # part of the body so push it back.
                 if not NLCRE.match(line):
+                    defect = errors.MissingHeaderBodySeparatorDefect()
+                    self.policy.handle_defect(self._cur, defect)
                     self._input.unreadline(line)
                 break
             headers.append(line)
@@ -488,12 +490,10 @@ class FeedParser:
                     self._cur.defects.append(defect)
                     continue
             # Split the line on the colon separating field name from value.
+            # There will always be a colon, because if there wasn't the part of
+            # the parser that calls us would have started parsing the body.
             i = line.find(':')
-            if i < 0:
-                defect = errors.MalformedHeaderDefect(line)
-                # XXX: fixme (defect not going through policy)
-                self._cur.defects.append(defect)
-                continue
+            assert i>0, "_parse_headers fed line with no : and no leading WS"
             lastheader = line[:i]
             lastvalue = [line]
         # Done with all the lines, so handle the last header.
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index ac6ee657452..c04952cad37 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -1960,15 +1960,27 @@ counter to RFC 2822, there's no separating newline here
     # test_parser.TestMessageDefectDetectionBase
     def test_first_line_is_continuation_header(self):
         eq = self.assertEqual
-        m = ' Line 1\nLine 2\nLine 3'
+        m = ' Line 1\nSubject: test\n\nbody'
         msg = email.message_from_string(m)
-        eq(msg.keys(), [])
-        eq(msg.get_payload(), 'Line 2\nLine 3')
+        eq(msg.keys(), ['Subject'])
+        eq(msg.get_payload(), 'body')
         eq(len(msg.defects), 1)
-        self.assertTrue(isinstance(msg.defects[0],
-                                   errors.FirstHeaderLineIsContinuationDefect))
+        self.assertDefectsEqual(msg.defects,
+                                 [errors.FirstHeaderLineIsContinuationDefect])
         eq(msg.defects[0].line, ' Line 1\n')
 
+    # test_parser.TestMessageDefectDetectionBase
+    def test_missing_header_body_separator(self):
+        # Our heuristic if we see a line that doesn't look like a header (no
+        # leading whitespace but no ':') is to assume that the blank line that
+        # separates the header from the body is missing, and to stop parsing
+        # headers and start parsing the body.
+        msg = self._str_msg('Subject: test\nnot a header\nTo: abc\n\nb\n')
+        self.assertEqual(msg.keys(), ['Subject'])
+        self.assertEqual(msg.get_payload(), 'not a header\nTo: abc\n\nb\n')
+        self.assertDefectsEqual(msg.defects,
+                                [errors.MissingHeaderBodySeparatorDefect])
+
 
 # Test RFC 2047 header encoding and decoding
 class TestRFC2047(TestEmailBase):
diff --git a/Lib/test/test_email/test_parser.py b/Lib/test/test_email/test_parser.py
index 864e4c1677f..f58e7c1208e 100644
--- a/Lib/test/test_email/test_parser.py
+++ b/Lib/test/test_email/test_parser.py
@@ -237,17 +237,33 @@ class TestMessageDefectDetectionBase:
                           policy=self.policy.clone(raise_on_defect=True))
 
     def test_first_line_is_continuation_header(self):
-        msg = self._str_msg(' Line 1\nLine 2\nLine 3')
-        self.assertEqual(msg.keys(), [])
-        self.assertEqual(msg.get_payload(), 'Line 2\nLine 3')
+        msg = self._str_msg(' Line 1\nSubject: test\n\nbody')
+        self.assertEqual(msg.keys(), ['Subject'])
+        self.assertEqual(msg.get_payload(), 'body')
         self.assertEqual(len(self.get_defects(msg)), 1)
-        self.assertTrue(isinstance(self.get_defects(msg)[0],
-                                   errors.FirstHeaderLineIsContinuationDefect))
+        self.assertDefectsEqual(self.get_defects(msg),
+                                 [errors.FirstHeaderLineIsContinuationDefect])
         self.assertEqual(self.get_defects(msg)[0].line, ' Line 1\n')
 
     def test_first_line_is_continuation_header_raise_on_defect(self):
         with self.assertRaises(errors.FirstHeaderLineIsContinuationDefect):
-            self._str_msg(' Line 1\nLine 2\nLine 3',
+            self._str_msg(' Line 1\nSubject: test\n\nbody\n',
+                          policy=self.policy.clone(raise_on_defect=True))
+
+    def test_missing_header_body_separator(self):
+        # Our heuristic if we see a line that doesn't look like a header (no
+        # leading whitespace but no ':') is to assume that the blank line that
+        # separates the header from the body is missing, and to stop parsing
+        # headers and start parsing the body.
+        msg = self._str_msg('Subject: test\nnot a header\nTo: abc\n\nb\n')
+        self.assertEqual(msg.keys(), ['Subject'])
+        self.assertEqual(msg.get_payload(), 'not a header\nTo: abc\n\nb\n')
+        self.assertDefectsEqual(self.get_defects(msg),
+                                [errors.MissingHeaderBodySeparatorDefect])
+
+    def test_missing_header_body_separator_raise_on_defect(self):
+        with self.assertRaises(errors.MissingHeaderBodySeparatorDefect):
+            self._str_msg('Subject: test\nnot a header\nTo: abc\n\nb\n',
                           policy=self.policy.clone(raise_on_defect=True))
 
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 512783a0c65..e8171ac7a59 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -49,6 +49,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #14925: email now registers a defect when the parser decides that there
+  is a missing header/body separator line.  MalformedHeaderDefect, which the
+  existing code would never actually generate, is deprecated.
+
 - Issue #10365: File open dialog now works instead of crashing
   even when parent window is closed. Patch by Roger Serwy.