diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py

index 737951e4b1b1..bc9c9b6241d4 100644

--- a/Lib/email/_header_value_parser.py

+++ b/Lib/email/_header_value_parser.py

@@ -1561,6 +1561,8 @@ def get_domain(value):

         token, value = get_dot_atom(value)

     except errors.HeaderParseError:

         token, value = get_atom(value)

+    if value and value[0] == '@':

+        raise errors.HeaderParseError('Invalid Domain')

     if leader is not None:

         token[:0] = [leader]

     domain.append(token)

diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py

index cdfa3729adc7..41ff6f8c000d 100644

--- a/Lib/email/_parseaddr.py

+++ b/Lib/email/_parseaddr.py

@@ -379,7 +379,12 @@ def getaddrspec(self):

         aslist.append('@')

         self.pos += 1

         self.gotonext()

-        return EMPTYSTRING.join(aslist) + self.getdomain()

+        domain = self.getdomain()

+        if not domain:

+            # Invalid domain, return an empty address instead of returning a

+            # local part to denote failed parsing.

+            return EMPTYSTRING

+        return EMPTYSTRING.join(aslist) + domain

     def getdomain(self):

         """Get the complete domain name from an address."""

@@ -394,6 +399,10 @@ def getdomain(self):

             elif self.field[self.pos] == '.':

                 self.pos += 1

                 sdlist.append('.')

+            elif self.field[self.pos] == '@':

+                # bpo-34155: Don't parse domains with two `@` like

+                # `a@malicious.org@important.com`.

+                return EMPTYSTRING

             elif self.field[self.pos] in self.atomends:

                 break

             else:

diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py

index a2c900fa7fd2..02ef3e1006c6 100644

--- a/Lib/test/test_email/test__header_value_parser.py

+++ b/Lib/test/test_email/test__header_value_parser.py

@@ -1418,6 +1418,16 @@ def test_get_addr_spec_dot_atom(self):

         self.assertEqual(addr_spec.domain, 'example.com')

         self.assertEqual(addr_spec.addr_spec, 'star.a.star@example.com')

+    def test_get_addr_spec_multiple_domains(self):

+        with self.assertRaises(errors.HeaderParseError):

+            parser.get_addr_spec('star@a.star@example.com')

+

+        with self.assertRaises(errors.HeaderParseError):

+            parser.get_addr_spec('star@a@example.com')

+

+        with self.assertRaises(errors.HeaderParseError):

+            parser.get_addr_spec('star@172.17.0.1@example.com')

+

     # get_obs_route

     def test_get_obs_route_simple(self):

diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py

index f97ccc6711cc..68d052279987 100644

--- a/Lib/test/test_email/test_email.py

+++ b/Lib/test/test_email/test_email.py

@@ -3035,6 +3035,20 @@ def test_parseaddr_empty(self):

         self.assertEqual(utils.parseaddr('<>'), ('', ''))

         self.assertEqual(utils.formataddr(utils.parseaddr('<>')), '')

+    def test_parseaddr_multiple_domains(self):

+        self.assertEqual(

+            utils.parseaddr('a@b@c'),

+            ('', '')

+        )

+        self.assertEqual(

+            utils.parseaddr('a@b.c@c'),

+            ('', '')

+        )

+        self.assertEqual(

+            utils.parseaddr('a@172.17.0.1@c'),

+            ('', '')

+        )

+

     def test_noquote_dump(self):

         self.assertEqual(

             utils.formataddr(('A Silly Person', 'person@dom.ain')),

diff --git a/Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst b/Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst

new file mode 100644

index 000000000000..50292e29ed1d

--- /dev/null

+++ b/Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst

@@ -0,0 +1 @@

+Fix parsing of invalid email addresses with more than one ``@`` (e.g. a@b@c.com.) to not return the part before 2nd ``@`` as valid email address. Patch by maxking & jpic.