diff --git a/dds_registration/core/app/backends.py b/dds_registration/core/app/backends.py
index e8f3c953..d6b9800f 100644
--- a/dds_registration/core/app/backends.py
+++ b/dds_registration/core/app/backends.py
@@ -10,10 +10,16 @@ class EmailBackend(ModelBackend):
     def authenticate(self, request, username=None, password=None, **kwargs):
         UserModel = get_user_model()
         try:
-            user = UserModel.objects.get(email=username)
+            user = UserModel.objects.get(email__iexact=username)
         except UserModel.DoesNotExist:
             return None
-        else:
-            if user.check_password(password):
-                return user
+        except UserModel.MultipleObjectsReturned:
+            # The unique constraint on email is case-sensitive, so case-variant
+            # duplicates can exist; disambiguate with an exact match.
+            try:
+                user = UserModel.objects.get(email=username)
+            except UserModel.DoesNotExist:
+                return None
+        if user.check_password(password):
+            return user
         return None
diff --git a/dds_registration/forms.py b/dds_registration/forms.py
index 785949d1..66cac789 100644
--- a/dds_registration/forms.py
+++ b/dds_registration/forms.py
@@ -1,7 +1,7 @@
 from captcha.fields import CaptchaField
 from django import forms
 from django.contrib.auth import get_user_model
-from django.contrib.auth.forms import UserCreationForm
+from django.contrib.auth.forms import UserChangeForm, UserCreationForm
 from django.core.exceptions import ValidationError
 from django.forms.models import ModelForm
 from django.utils.safestring import mark_safe
@@ -178,8 +178,11 @@ class Meta:
         fields = "__all__"
 
 
-class UserAdminForm(ModelForm):
-    class Meta:
+class UserAdminForm(UserChangeForm):
+    # Must extend UserChangeForm, not ModelForm: a plain ModelForm renders the raw
+    # password hash as an editable text input, and saving it overwrites the hash
+    # with plaintext, permanently locking the user out.
+    class Meta(UserChangeForm.Meta):
         model = User
         widgets = {
             "first_name": textInputWidget,
diff --git a/tests/test_admin_user_form.py b/tests/test_admin_user_form.py
new file mode 100644
index 00000000..843637d4
--- /dev/null
+++ b/tests/test_admin_user_form.py
@@ -0,0 +1,23 @@
+import pytest
+from django.contrib.auth import get_user_model
+from django.contrib.auth.forms import ReadOnlyPasswordHashField
+
+from dds_registration.forms import UserAdminForm
+
+
+def test_password_field_is_readonly_hash_field():
+    field = UserAdminForm.base_fields["password"]
+    assert isinstance(field, ReadOnlyPasswordHashField)
+
+
+@pytest.mark.django_db
+def test_admin_form_ignores_submitted_password_value():
+    User = get_user_model()
+    user = User.objects.create_user(
+        username="bo@example.com",
+        email="bo@example.com",
+        password="original-password",
+    )
+    original_hash = user.password
+    form = UserAdminForm(data={"password": "!Temporal2026"}, instance=user)
+    assert form["password"].value() == original_hash
diff --git a/tests/test_email_backend.py b/tests/test_email_backend.py
new file mode 100644
index 00000000..bea67e46
--- /dev/null
+++ b/tests/test_email_backend.py
@@ -0,0 +1,45 @@
+import pytest
+from django.contrib.auth import authenticate, get_user_model
+
+
+def make_user(email, password="correct-horse"):
+    return get_user_model().objects.create_user(username=email, email=email, password=password)
+
+
+@pytest.mark.django_db
+def test_login_email_is_case_insensitive():
+    make_user("bo@example.com")
+    user = authenticate(None, username="Bo@Example.COM", password="correct-horse")
+    assert user is not None
+    assert user.email == "bo@example.com"
+
+
+@pytest.mark.django_db
+def test_mixed_case_stored_email_accepts_lowercase_login():
+    make_user("Jane.Doe@example.com")
+    user = authenticate(None, username="jane.doe@example.com", password="correct-horse")
+    assert user is not None
+    assert user.email == "Jane.Doe@example.com"
+
+
+@pytest.mark.django_db
+def test_wrong_password_still_rejected():
+    make_user("bo@example.com")
+    assert authenticate(None, username="Bo@Example.com", password="wrong") is None
+
+
+@pytest.mark.django_db
+def test_unknown_email_rejected():
+    assert authenticate(None, username="nobody@example.com", password="whatever") is None
+
+
+@pytest.mark.django_db
+def test_case_duplicate_accounts_fall_back_to_exact_match():
+    # The unique constraint on email is case-sensitive, so case-variant
+    # duplicates can exist; each must still log into its own account.
+    make_user("bo@example.com", password="lower-pass")
+    make_user("BO@example.com", password="upper-pass")
+    user = authenticate(None, username="bo@example.com", password="lower-pass")
+    assert user is not None and user.email == "bo@example.com"
+    user = authenticate(None, username="BO@example.com", password="upper-pass")
+    assert user is not None and user.email == "BO@example.com"