diff --git a/changelog.d/11547.bugfix b/changelog.d/11547.bugfix
new file mode 100644
index 000000000000..3950c4c8d30c
--- /dev/null
+++ b/changelog.d/11547.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.17.0 where a pusher created for an email with capital letters would fail to be created.
diff --git a/synapse/push/pusherpool.py b/synapse/push/pusherpool.py
index 26735447a6f1..7912311d2401 100644
--- a/synapse/push/pusherpool.py
+++ b/synapse/push/pusherpool.py
@@ -27,6 +27,7 @@
 from synapse.replication.http.push import ReplicationRemovePusherRestServlet
 from synapse.types import JsonDict, RoomStreamToken
 from synapse.util.async_helpers import concurrently_execute
+from synapse.util.threepids import canonicalise_email
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -113,7 +114,9 @@ async def add_pusher(
         """
 
         if kind == "email":
-            email_owner = await self.store.get_user_id_by_threepid("email", pushkey)
+            email_owner = await self.store.get_user_id_by_threepid(
+                "email", canonicalise_email(pushkey)
+            )
             if email_owner != user_id:
                 raise SynapseError(400, "Email not found", Codes.THREEPID_NOT_FOUND)
 
diff --git a/synapse/storage/databases/main/monthly_active_users.py b/synapse/storage/databases/main/monthly_active_users.py
index b5284e4f6783..3c98ef876f8c 100644
--- a/synapse/storage/databases/main/monthly_active_users.py
+++ b/synapse/storage/databases/main/monthly_active_users.py
@@ -18,6 +18,7 @@
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import DatabasePool, make_in_list_sql_clause
 from synapse.util.caches.descriptors import cached
+from synapse.util.threepids import canonicalise_email
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -103,7 +104,7 @@ async def get_registered_reserved_users(self) -> List[str]:
             : self.hs.config.server.max_mau_value
         ]:
             user_id = await self.hs.get_datastore().get_user_id_by_threepid(
-                tp["medium"], tp["address"]
+                tp["medium"], canonicalise_email(tp["address"])
             )
             if user_id:
                 users.append(user_id)
diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index e1ddf0691646..86c34257168c 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -856,7 +856,8 @@ async def get_user_id_by_threepid(self, medium: str, address: str) -> Optional[s
 
         Args:
             medium: threepid medium e.g. email
-            address: threepid address e.g. me@example.com
+            address: threepid address e.g. me@example.com. This must already be
+                in canonical form.
 
         Returns:
             The user ID or None if no user id/threepid mapping exists
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 294d429ce12b..eea675991cbc 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -1550,7 +1550,8 @@ def test_create_user_email_notif_for_new_users(self):
         # Create user
         body = {
             "password": "abc123",
-            "threepids": [{"medium": "email", "address": "bob@bob.bob"}],
+            # Note that the given email is not in canonical form.
+            "threepids": [{"medium": "email", "address": "Bob@bob.bob"}],
         }
 
         channel = self.make_request(