diff --git a/common/djangoapps/student/models.py b/common/djangoapps/student/models.py
index 0c7ae47997cd..8cd555e3f2e0 100644
--- a/common/djangoapps/student/models.py
+++ b/common/djangoapps/student/models.py
@@ -66,6 +66,7 @@
 
 from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
 from openedx.core.djangoapps.request_cache import clear_cache, get_cache
+from openedx.core.djangoapps.signals.signals import USER_ACCOUNT_ACTIVATED
 from openedx.core.djangoapps.site_configuration import helpers as configuration_helpers
 from openedx.core.djangoapps.xmodule_django.models import NoneToEmptyManager
 from openedx.core.djangolib.model_mixins import DeletableByUserValue
@@ -728,6 +729,7 @@ def activate(self):
         self.user.is_active = True
         self._track_activation()
         self.user.save()
+        USER_ACCOUNT_ACTIVATED.send_robust(self.__class__, user=self.user)
         log.info(u'User %s (%s) account is successfully activated.', self.user.username, self.user.email)
 
     def _track_activation(self):
diff --git a/common/djangoapps/student/tests/test_activate_account.py b/common/djangoapps/student/tests/test_activate_account.py
index 099516b53a4f..29c74a6cddd9 100644
--- a/common/djangoapps/student/tests/test_activate_account.py
+++ b/common/djangoapps/student/tests/test_activate_account.py
@@ -98,6 +98,19 @@ def test_activation_with_keys(self, mock_segment_identify):
             expected_segment_mailchimp_list
         )
 
+    @patch('student.models.USER_ACCOUNT_ACTIVATED')
+    def test_activation_signal(self, mock_signal):
+        """
+        Verify that USER_ACCOUNT_ACTIVATED is emitted upon account email activation.
+
+        Appsembler: This is a custom code to be pushed upstream.
+        """
+        assert not self.user.is_active, 'Ensure that the user starts inactive'
+        assert not mock_signal.send_robust.call_count, 'Ensure no signal is fired before activation'
+        self.registration.activate()  # Until you explicitly activate it
+        assert self.user.is_active, 'Sanity check for .activate()'
+        mock_signal.send_robust.assert_called_once_with(Registration, user=self.user), 'Ensure the signal is emitted'
+
     @override_settings(LMS_SEGMENT_KEY="testkey")
     @patch('student.models.analytics.identify')
     def test_activation_without_mailchimp_key(self, mock_segment_identify):
diff --git a/common/lib/capa/capa/capa_problem.py b/common/lib/capa/capa/capa_problem.py
index c13567c82d3e..78ae3b4daa92 100644
--- a/common/lib/capa/capa/capa_problem.py
+++ b/common/lib/capa/capa/capa_problem.py
@@ -60,6 +60,7 @@
 
 # These should be removed from HTML output, including all subelements
 html_problem_semantics = [
+    "additional_answer",
     "codeparam",
     "responseparam",
     "answer",
diff --git a/common/lib/capa/capa/tests/test_capa_problem.py b/common/lib/capa/capa/tests/test_capa_problem.py
index 59ca1d442144..85016058bb93 100644
--- a/common/lib/capa/capa/tests/test_capa_problem.py
+++ b/common/lib/capa/capa/tests/test_capa_problem.py
@@ -185,6 +185,23 @@ def test_multiple_descriptions(self):
             }
         )
 
+    def test_additional_answer_is_skipped_from_resulting_html(self):
+        """Tests that additional_answer element is not present in transformed HTML"""
+        xml = """
+        <problem>
+            <p>Be sure to check your spelling.</p>
+            <stringresponse answer="War" type="ci">
+                <label>___ requires sacrifices.</label>
+                <description>Anyone who looks the world as if it was a game of chess deserves to lose.</description>
+                <additional_answer answer="optional acceptable variant of the correct answer"/>
+                <textline size="40"/>
+            </stringresponse>
+        </problem>
+        """
+        problem = new_loncapa_problem(xml)
+        self.assertEqual(len(problem.extracted_tree.xpath('//additional_answer')), 0)
+        self.assertNotIn('additional_answer', problem.get_html())
+
     def test_non_accessible_inputtype(self):
         """
         Verify that tag with question text is not removed when inputtype is not fully accessible.
diff --git a/openedx/core/djangoapps/appsembler/api/tests/test_user_api.py b/openedx/core/djangoapps/appsembler/api/tests/test_user_api.py
index cf50d520608c..e23d05c7c160 100644
--- a/openedx/core/djangoapps/appsembler/api/tests/test_user_api.py
+++ b/openedx/core/djangoapps/appsembler/api/tests/test_user_api.py
@@ -32,6 +32,11 @@
 @mock.patch(APPSEMBLER_API_VIEWS_MODULE + '.UserIndexViewSet.throttle_classes', [])
 class UserIndexViewSetTest(TestCase):
 
+    # Fixtures to be used for filtering
+    JANE_DUE_USERNAME = 'jane.due'
+    JANE_DUE_EMAIL = '{username}@user.api.example.com'.format(username=JANE_DUE_USERNAME)
+    NON_USER_EMAIL = 'not.for.a.user@user.api.example.com'
+
     def setUp(self):
         """
         Set up test data for site isolation
@@ -51,7 +56,12 @@ def setUp(self):
         self.my_site_org = OrganizationFactory(sites=[self.my_site])
 
         # Set up users and enrollments for 'my site'
-        self.my_site_users = [UserFactory() for i in range(3)]
+        self.my_site_users = [
+            UserFactory.create(email=self.JANE_DUE_EMAIL, username=self.JANE_DUE_USERNAME),
+            UserFactory.create(),
+            UserFactory.create(),
+        ]
+
         for user in self.my_site_users:
             UserOrganizationMappingFactory(user=user,
                                            organization=self.my_site_org)
@@ -90,6 +100,32 @@ def test_get_all_users_for_site(self):
         user_ids = [rec['id'] for rec in results]
         assert set(user_ids) == set([obj.id for obj in expected_users])
 
+    @ddt.unpack
+    @ddt.data(
+        {'email': JANE_DUE_EMAIL.lower(), 'expected_count': 1, 'msg': 'Should find Jane (lower case) in the users'},
+        {'email': JANE_DUE_EMAIL.upper(), 'expected_count': 1, 'msg': 'Should find Jane (upper case) in the users'},
+        {'email': JANE_DUE_USERNAME, 'expected_count': 0, 'msg': 'Should not do partial matching'},
+        {'email': NON_USER_EMAIL, 'expected_count': 0, 'msg': 'Should not match any user.'},
+    )
+    def test_filter_by_email(self, email, expected_count, msg):
+        """
+        Test the email filters matching.
+        """
+        url = reverse('tahoe-api:v1:users-list')
+        request = APIRequestFactory().get(url, {'email_exact': email})
+        request.META['HTTP_HOST'] = self.my_site.domain
+        force_authenticate(request, user=self.caller)
+
+        view = resolve(url).func
+        response = view(request)
+        response.render()
+        results = response.data['results']
+
+        assert len(results) == expected_count, msg
+        if expected_count:
+            # Ignore the email case
+            assert results[0]['email'].lower() == email.lower(), msg
+
     @skip("Need to implement user filter")
     def test_get_all_enrolled_learners_for_site(self):
 
diff --git a/openedx/core/djangoapps/appsembler/api/v1/filters.py b/openedx/core/djangoapps/appsembler/api/v1/filters.py
index e68621905d9d..904d62e86fa5 100644
--- a/openedx/core/djangoapps/appsembler/api/v1/filters.py
+++ b/openedx/core/djangoapps/appsembler/api/v1/filters.py
@@ -1,5 +1,6 @@
 
 import django_filters
+from django.contrib.auth import get_user_model
 from opaque_keys.edx.keys import CourseKey
 from openedx.core.djangoapps.content.course_overviews.models import (
     CourseOverview,
@@ -68,3 +69,15 @@ def filter_course_id(self, queryset, name, value):
     class Meta:
         model = CourseEnrollment
         fields = ['course_id', 'user_id', 'username', 'is_active', ]
+
+
+class UserIndexFilter(django_filters.FilterSet):
+    '''Provides filtering for the User model objects in the UserIndexViewSet.
+
+    '''
+
+    email_exact = django_filters.CharFilter(name='email', lookup_expr='iexact')
+
+    class Meta:
+        model = get_user_model()
+        fields = ['email_exact']
diff --git a/openedx/core/djangoapps/appsembler/api/v1/views.py b/openedx/core/djangoapps/appsembler/api/v1/views.py
index a74f29c6f17c..e399de1109d6 100644
--- a/openedx/core/djangoapps/appsembler/api/v1/views.py
+++ b/openedx/core/djangoapps/appsembler/api/v1/views.py
@@ -50,7 +50,8 @@
 from openedx.core.djangoapps.appsembler.api.v1.api import enroll_learners_in_course
 from openedx.core.djangoapps.appsembler.api.v1.filters import (
     CourseEnrollmentFilter,
-    CourseOverviewFilter
+    CourseOverviewFilter,
+    UserIndexFilter,
 )
 from openedx.core.djangoapps.appsembler.api.v1.pagination import (
     TahoeLimitOffsetPagination
@@ -397,6 +398,7 @@ class UserIndexViewSet(TahoeAuthMixin, viewsets.ReadOnlyModelViewSet):
     serializer_class = UserIndexSerializer
     throttle_classes = (TahoeAPIUserThrottle,)
     filter_backends = (DjangoFilterBackend, )
+    filter_class = UserIndexFilter
 
     def get_queryset(self):
         site = django.contrib.sites.shortcuts.get_current_site(self.request)
diff --git a/openedx/core/djangoapps/signals/signals.py b/openedx/core/djangoapps/signals/signals.py
index 90b9fa08a61c..26592fa32667 100644
--- a/openedx/core/djangoapps/signals/signals.py
+++ b/openedx/core/djangoapps/signals/signals.py
@@ -21,5 +21,7 @@
     ]
 )
 
-# Signal that indicates that a user has become verified
+# Signal that indicates that a user has become verified for certificate purposes
 LEARNER_NOW_VERIFIED = Signal(providing_args=['user'])
+
+USER_ACCOUNT_ACTIVATED = Signal(providing_args=["user"])  # Signal indicating email verification
diff --git a/tox.ini b/tox.ini
index d82678c70f02..79de0948c9e5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -68,6 +68,7 @@ commands =
     bash scripts/upgrade_pysqlite.sh
     {env:TRAVIS_FIXES}
     pytest \
+        common/djangoapps/student/tests/test_activate_account.py \
         common/djangoapps/util/tests/test_milestones_helpers.py \
         common/lib/xmodule/xmodule/modulestore/tests/test_split_mongo_mongo_connection.py