diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9666e40..756d06f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to
 
 ## [Unreleased]
 
+- 🐛(mailbox) fix case-sensitive duplicates on display names
 - ✨(mailbox) synchronize password of newly created mailbox with Dimail's
 
 ## [1.19.1] - 2025-09-19
diff --git a/src/backend/mailbox_manager/admin.py b/src/backend/mailbox_manager/admin.py
index 1ccfef2..c9f9a93 100644
--- a/src/backend/mailbox_manager/admin.py
+++ b/src/backend/mailbox_manager/admin.py
@@ -206,7 +206,7 @@ class MailboxAdmin(UserAdmin):
 
     list_display = ("__str__", "domain", "status", "updated_at")
     list_filter = ("status",)
-    search_fields = ("local_part", "domain__name")
+    search_fields = ("local_part", "domain__name", "first_name", "last_name")
     readonly_fields = ["updated_at"]
 
     fieldsets = None
diff --git a/src/backend/mailbox_manager/migrations/0027_remove_mailbox_unique_ox_display_name_and_more.py b/src/backend/mailbox_manager/migrations/0027_remove_mailbox_unique_ox_display_name_and_more.py
new file mode 100644
index 0000000..6a15e1a
--- /dev/null
+++ b/src/backend/mailbox_manager/migrations/0027_remove_mailbox_unique_ox_display_name_and_more.py
@@ -0,0 +1,22 @@
+# Generated by Django 5.2.7 on 2025-10-21 15:49
+
+import django.db.models.functions.text
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('mailbox_manager', '0026_alter_mailbox_unique_together_and_more'),
+    ]
+
+    operations = [
+        migrations.RemoveConstraint(
+            model_name='mailbox',
+            name='unique_ox_display_name',
+        ),
+        migrations.AddConstraint(
+            model_name='mailbox',
+            constraint=models.UniqueConstraint(django.db.models.functions.text.Lower('first_name'), django.db.models.functions.text.Lower('last_name'), models.F('domain'), name='unique_ox_display_name', violation_error_message='Mailbox with this First name, Last name and Domain already exists.'),
+        ),
+    ]
diff --git a/src/backend/mailbox_manager/models.py b/src/backend/mailbox_manager/models.py
index 3ba754e..86710f4 100644
--- a/src/backend/mailbox_manager/models.py
+++ b/src/backend/mailbox_manager/models.py
@@ -10,6 +10,7 @@ from django.contrib.auth.base_user import AbstractBaseUser
 from django.contrib.sites.models import Site
 from django.core import exceptions, mail, validators
 from django.db import models
+from django.db.models.functions import Lower
 from django.template.loader import render_to_string
 from django.utils.text import slugify
 from django.utils.translation import get_language, gettext, override
@@ -308,12 +309,17 @@ class Mailbox(AbstractBaseUser, BaseModel):
                 fields=["local_part", "domain"], name="unique_username"
             ),
             models.UniqueConstraint(
-                fields=["first_name", "last_name", "domain"],
+                Lower("first_name"),
+                Lower("last_name"),
+                "domain",
                 name="unique_ox_display_name",
+                violation_error_message="Mailbox with this First name, \
+Last name and Domain already exists.",
             ),
             # Display name in OpenXChange must be unique
             # To avoid sending failing requests to dimail,
             # we impose uniqueness here too
+            # And compare to lowercase to enforce case-insensitive uniqueness
         ]
         ordering = ["-created_at"]
 
diff --git a/src/backend/mailbox_manager/tests/api/mailboxes/test_api_mailboxes_create.py b/src/backend/mailbox_manager/tests/api/mailboxes/test_api_mailboxes_create.py
index f2f419f..e9bbc80 100644
--- a/src/backend/mailbox_manager/tests/api/mailboxes/test_api_mailboxes_create.py
+++ b/src/backend/mailbox_manager/tests/api/mailboxes/test_api_mailboxes_create.py
@@ -77,7 +77,7 @@ def test_api_mailboxes__create_viewer_failure(mailbox_data):
 def test_api_mailboxes__create_display_name_must_be_unique():
     """Primary id on OpenXchange is display name (first_name + last_name).
     It needs to be unique on each context. We don't track context info for now
-    but can impose uniqueness by domain."""
+    but can impose case-insensitive uniqueness by domain."""
     access = factories.MailDomainAccessFactory(role=enums.MailDomainRoleChoices.OWNER)
     existing_mailbox = factories.MailboxFactory(domain=access.domain)
 
@@ -86,8 +86,8 @@ def test_api_mailboxes__create_display_name_must_be_unique():
 
     new_mailbox_data = {
         "local_part": "something_else",
-        "first_name": existing_mailbox.first_name,
-        "last_name": existing_mailbox.last_name,
+        "first_name": existing_mailbox.first_name.upper(),  # ensure case-insensitivity
+        "last_name": existing_mailbox.last_name.lower(),
     }
     response = client.post(
         f"/api/v1.0/mail-domains/{access.domain.slug}/mailboxes/",