diff --git a/zerver/models.py b/zerver/models.py
index dacac37fdb..060ad50170 100644
--- a/zerver/models.py
+++ b/zerver/models.py
@@ -1551,6 +1551,10 @@ def active_user_ids(realm_id: int) -> List[int]:
     ).values_list('id', flat=True)
     return list(query)
 
+def get_membership_realms(email: str) -> List[Realm]:
+    profiles = UserProfile.objects.select_related('realm').filter(email__iexact=email.strip())
+    return [profile.realm for profile in profiles]
+
 @cache_with_key(bot_dicts_in_realm_cache_key, timeout=3600*24*7)
 def get_bot_dicts_in_realm(realm: Realm) -> List[Dict[str, Any]]:
     return UserProfile.objects.filter(realm=realm, is_bot=True).values(*bot_dict_fields)
diff --git a/zerver/tests/test_users.py b/zerver/tests/test_users.py
index 013502d9ca..3a66b247f0 100644
--- a/zerver/tests/test_users.py
+++ b/zerver/tests/test_users.py
@@ -20,7 +20,8 @@ from zerver.lib.test_runner import slow
 from zerver.models import UserProfile, Recipient, \
     Realm, RealmDomain, UserActivity, \
     get_user, get_realm, get_client, get_stream, get_stream_recipient, \
-    Message, get_context_for_message, ScheduledEmail
+    Message, get_context_for_message, ScheduledEmail, \
+    get_membership_realms
 
 from zerver.lib.avatar import avatar_url
 from zerver.lib.email_mirror import create_missed_message_address
@@ -329,6 +330,27 @@ class UserProfileTest(ZulipTestCase):
         self.assertEqual(result[cordelia].email, cordelia)
         self.assertEqual(result[webhook_bot].email, webhook_bot)
 
+    def test_get_membership_realms(self) -> None:
+        zulip_realm = get_realm("zulip")
+        lear_realm = get_realm("lear")
+
+        email = "cordelia@zulip.com"
+        realms = get_membership_realms(email)
+        self.assert_length(realms, 2)
+        self.assertIn(zulip_realm, realms)
+        self.assertIn(lear_realm, realms)
+
+        email = "CORDelia@zulip.com"
+        realms = get_membership_realms(email)
+        self.assert_length(realms, 2)
+        self.assertIn(zulip_realm, realms)
+        self.assertIn(lear_realm, realms)
+
+        email = "IAGO@ZULIP.COM"
+        realms = get_membership_realms(email)
+        self.assert_length(realms, 1)
+        self.assertIn(zulip_realm, realms)
+
 class ActivateTest(ZulipTestCase):
     def test_basics(self) -> None:
         user = self.example_user('hamlet')