diff --git a/common/djangoapps/student/models.py b/common/djangoapps/student/models.py
index a332d2f96292..a513894c3f9a 100644
--- a/common/djangoapps/student/models.py
+++ b/common/djangoapps/student/models.py
@@ -55,7 +55,14 @@
 from six.moves.urllib.parse import urlencode
 from slumber.exceptions import HttpClientError, HttpServerError
 from user_util import user_util
-from organizations.models import UserOrganizationMapping, OrganizationCourse
+from organizations.models import OrganizationCourse
+
+from tahoe_sites.api import (
+    deprecated_is_existing_email_but_not_linked_yet,
+    get_organization_user_by_email,
+    get_organization_user_by_username_or_email,
+    is_exist_organization_user_by_email,
+)
 from openedx.core.djangoapps.theming.helpers import (
     get_current_request,
     get_current_site,
@@ -331,14 +338,11 @@ def email_exists_or_retired(email, check_for_new_site=False):
     """
     if settings.FEATURES.get('APPSEMBLER_MULTI_TENANT_EMAILS', False):
         if check_for_new_site:
-            exists = User.objects.filter(
-                email=email,
-                userorganizationmapping__isnull=True,  # Allow learners to signup for trial site, but ensure the trial
-                                                       # workflow is completed.
-            ).exists()
+            # Allow learners to signup for trial site, but ensure the trial workflow is completed.
+            exists = deprecated_is_existing_email_but_not_linked_yet(email=email)
         else:
             current_org = get_current_organization()
-            exists = current_org.userorganizationmapping_set.filter(user__email=email).exists()
+            exists = is_exist_organization_user_by_email(email=email, organization=current_org)
     else:
         exists = User.objects.filter(email=email).exists()
     check_within_organization = not check_for_new_site  # Allow existing learners to spin their new Tahoe trial
@@ -1630,9 +1634,9 @@ def enroll_by_email_in_organization(cls, email, course_id, mode=None, ignore_err
         try:
             site = get_current_site()
             organization = get_organization_for_site(site)
-            user = organization.userorganizationmapping_set.get(user__email=email).user
+            user = get_organization_user_by_email(email=email, organization=organization)
             return cls.enroll(user, course_id, mode)
-        except UserOrganizationMapping.DoesNotExist:
+        except User.DoesNotExist:
             err_msg = u"Tried to enroll email {} into course {}, but user not found"
             log.error(err_msg.format(email, course_id))
             if ignore_errors:
@@ -2494,10 +2498,10 @@ def get_user_by_username_or_email_inside_organization(username_or_email):
     # there should be one user with either username or email equal to username_or_email
     site = get_current_site()
     organization = get_organization_for_site(site)
-    try:
-        user = organization.userorganizationmapping_set.get(Q(user__email=username_or_email) | Q(user__username=username_or_email)).user
-    except UserOrganizationMapping.DoesNotExist:
-        raise User.DoesNotExist
+    user = get_organization_user_by_username_or_email(
+        username_or_email=username_or_email,
+        organization=organization
+    )
 
     if user.username == username_or_email:
         UserRetirementRequest = apps.get_model('user_api', 'UserRetirementRequest')
diff --git a/common/djangoapps/student/views/management.py b/common/djangoapps/student/views/management.py
index ad4e8cd1ecc1..57a869e7ca80 100644
--- a/common/djangoapps/student/views/management.py
+++ b/common/djangoapps/student/views/management.py
@@ -34,6 +34,7 @@
 from opaque_keys.edx.keys import CourseKey
 from pytz import UTC
 from six import text_type
+from tahoe_sites.api import is_exist_organization_user_by_email
 
 import track.views
 from bulk_email.models import Optout
@@ -753,7 +754,7 @@ def confirm_email_change(request, key):
 
         if settings.FEATURES.get('APPSEMBLER_MULTI_TENANT_EMAILS', False):
             current_org = get_current_organization()
-            email_exists = len(current_org.userorganizationmapping_set.filter(user__email=pec.new_email)) != 0
+            email_exists = is_exist_organization_user_by_email(email=pec.new_email, organization=current_org)
         else:
             email_exists = len(User.objects.filter(email=pec.new_email)) != 0
 
diff --git a/common/djangoapps/third_party_auth/utils.py b/common/djangoapps/third_party_auth/utils.py
index 4462aa350968..0d9554d1df57 100644
--- a/common/djangoapps/third_party_auth/utils.py
+++ b/common/djangoapps/third_party_auth/utils.py
@@ -6,6 +6,7 @@
 
 from django.conf import settings
 from django.contrib.auth.models import User
+from tahoe_sites.api import is_exist_organization_user_by_email
 
 from openedx.core.djangoapps.appsembler.sites.utils import get_current_organization
 
@@ -35,7 +36,7 @@ def user_exists(details):
             current_org = get_current_organization()
 
             if email:
-                return current_org.userorganizationmapping_set.filter(user__email=email).exists()
+                return is_exist_organization_user_by_email(email=email, organization=current_org)
             elif username:
                 try:
                     user = User.objects.get(username=username)
diff --git a/requirements/edx/appsembler.txt b/requirements/edx/appsembler.txt
index 683c37089ab8..c1f31d044d88 100644
--- a/requirements/edx/appsembler.txt
+++ b/requirements/edx/appsembler.txt
@@ -22,7 +22,8 @@ https://github.com/edx-solutions/xblock-google-drive/archive/589d9f51f9b.tar.gz
 
 # Tahoe plugins and customizations
 django-tiers==0.2.4
-tahoe-sites==0.1.5
+# tahoe-sites==0.1.5 plus new APIs
+-e git+https://github.com/appsembler/tahoe-sites.git@2bffb54a96b469005d5f397a400b74a8af4d05db#egg=tahoe-sites==0.1.5-newapis
 tahoe-lti==0.3.0
 site-configuration-client==0.1.3