diff --git a/domain_service.py b/domain_service.py
index d2890c5..55a91b0 100644
--- a/domain_service.py
+++ b/domain_service.py
@@ -7,6 +7,7 @@ from domain_runtime import domain_manager
 import json
 from kubernetes.client.rest import ApiException
 from kubernetes_service import custom_objects_api, k8s_manager
+from namespace_utils import user_namespace
 import re
 from runtime_config import (
     NODE_IP,
@@ -325,7 +326,7 @@ def cleanup_orphaned_ingressroutes():
             for domain, username in db_domains.items():
                 if not domain or not username:
                     continue
-                namespace = f"user-{username}".lower()
+                namespace = user_namespace(username)
                 subdomain = domain.split('.')[0]
                 ingressroute_name = f"{subdomain}-ingress"
 
@@ -590,7 +591,7 @@ def link_domain_to_server(domain_id: str, server_id: str) -> bool:
                 return False
 
             username = user['username']
-            namespace = (server.get('namespace') or f"user-{username}").lower()
+            namespace = server.get('namespace') or user_namespace(username)
             domain_host = domain.get('full_domain') or domain.get('domain')
             if not domain_host:
                 logger.error("Domain record has no hostname: %s", domain_id)
@@ -675,7 +676,7 @@ def unlink_domain_from_server(domain_id: str) -> bool:
 
             if user:
                 username = user['username']
-                namespace = ((server or {}).get('namespace') or f"user-{username}").lower()
+                namespace = (server or {}).get('namespace') or user_namespace(username)
 
                 # Delete IngressRoute in Kubernetes
                 if not delete_traefik_ingressroute(domain=domain_host, namespace=namespace):
diff --git a/kubernetes_service.py b/kubernetes_service.py
index 891420c..9de042e 100644
--- a/kubernetes_service.py
+++ b/kubernetes_service.py
@@ -3,6 +3,7 @@ from datetime import datetime
 from kubernetes import client, config
 from kubernetes.client.rest import ApiException
 from kubernetes.stream import stream
+from namespace_utils import is_valid_namespace_name
 import os
 import random
 from runtime_config import (
@@ -62,8 +63,9 @@ class KubernetesManager:
             return False
 
     def create_namespace(self, namespace_name: str, labels: Dict = None) -> bool:
-        # Kubernetes namespaces MUST be lowercase
-        namespace_name = namespace_name.lower()
+        if not is_valid_namespace_name(namespace_name):
+            logger.error("Refusing to create invalid Kubernetes namespace name: %r", namespace_name)
+            return False
 
         if not self.connected:
             logger.info(f"⚠ Kubernetes not connected, skipping namespace creation for {namespace_name}")
diff --git a/namespace_utils.py b/namespace_utils.py
new file mode 100644
index 0000000..80c32e1
--- /dev/null
+++ b/namespace_utils.py
@@ -0,0 +1,43 @@
+"""Helpers for translating account names to Kubernetes namespace names."""
+
+from __future__ import annotations
+
+import hashlib
+import re
+
+
+_DNS_LABEL = re.compile(r"^[a-z0-9](?:[-a-z0-9]*[a-z0-9])?$")
+_INVALID_DNS_LABEL_CHARS = re.compile(r"[^a-z0-9-]+")
+
+
+def is_valid_namespace_name(namespace_name: str) -> bool:
+    """Return whether a name meets Kubernetes DNS-label constraints."""
+    return (
+        isinstance(namespace_name, str)
+        and len(namespace_name) <= 63
+        and bool(_DNS_LABEL.fullmatch(namespace_name))
+    )
+
+
+def user_namespace(username: str) -> str:
+    """Return a stable, DNS-label-safe namespace for a username.
+
+    Existing valid usernames retain their current namespace. Names that need
+    normalization receive a short digest so normalization cannot silently
+    merge accounts such as ``miki.dz08`` and ``miki-dz08``.
+    """
+    normalized_username = str(username).strip().lower()
+    if not normalized_username:
+        raise ValueError("Username must not be empty")
+
+    candidate = f"user-{normalized_username}"
+    if is_valid_namespace_name(candidate):
+        return candidate
+
+    safe_username = _INVALID_DNS_LABEL_CHARS.sub("-", normalized_username)
+    safe_username = re.sub(r"-+", "-", safe_username).strip("-") or "user"
+    digest = hashlib.sha256(normalized_username.encode("utf-8")).hexdigest()[:8]
+    suffix = f"-{digest}"
+    max_base_length = 63 - len("user-") - len(suffix)
+    safe_username = safe_username[:max_base_length].rstrip("-") or "user"
+    return f"user-{safe_username}{suffix}"
diff --git a/routes/servers.py b/routes/servers.py
index cba8712..fa2124c 100644
--- a/routes/servers.py
+++ b/routes/servers.py
@@ -6,6 +6,7 @@ from flask import Blueprint, jsonify, request
 import json
 from urllib.parse import urlsplit
 from kubernetes_service import k8s_manager
+from namespace_utils import user_namespace
 import requests
 from werkzeug.utils import secure_filename
 from runtime_config import (
@@ -379,7 +380,7 @@ def download_plugin_to_server():
                     plugin_response.close()
 
             # Upload to server
-            namespace = f"user-{user['username']}".lower()
+            namespace = user_namespace(user['username'])
             pods = k8s_manager.get_pods_for_server(namespace, server_id)
 
             if not pods:
diff --git a/server_lifecycle.py b/server_lifecycle.py
index cd9d648..fb8241c 100644
--- a/server_lifecycle.py
+++ b/server_lifecycle.py
@@ -4,6 +4,7 @@
 from database_service import database_connection
 from kubernetes import client
 from kubernetes_service import apps_v1, custom_objects_api, k8s_manager, v1
+from namespace_utils import user_namespace
 from runtime_config import (
     logger,
 )
@@ -59,7 +60,7 @@ def delete_server(server_id: str, user_id: str) -> bool:
                 pass
             return True
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
 
         try:
             custom_objects_api.delete_namespaced_custom_object(
@@ -165,7 +166,7 @@ def start_server(server_id: str, user_id: str) -> bool:
             update_server_status(server_id, 'Running')
             return True
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
 
         try:
             patch = {'spec': {'runStrategy': 'Always'}}
@@ -232,7 +233,7 @@ def stop_server(server_id: str, user_id: str) -> bool:
             update_server_status(server_id, 'Stopped')
             return True
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
 
         try:
             patch = {'spec': {'runStrategy': 'Halted'}}
@@ -317,7 +318,7 @@ def restart_server(server_id: str, user_id: str, skip_checks: bool = False) -> b
             update_server_status(server_id, 'Running')
             return True
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
         update_server_status(server_id, 'Restarting')
 
         try:
@@ -721,7 +722,7 @@ def adjust_server_parameters(server_id: str, user_id: str, new_cpu: str, new_ram
             conn.commit()
 
         # Update server resources in Kubernetes
-        namespace = f"user-{user['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(user['username'])
         if k8s_manager.connected:
             if not update_server_resources_in_k8s(server, new_cpu, new_ram, new_storage, namespace):
                 logger.warning(f"Failed to update server resources in K8s, but database was updated")
diff --git a/server_provisioning.py b/server_provisioning.py
index 9db6688..a0af31e 100644
--- a/server_provisioning.py
+++ b/server_provisioning.py
@@ -6,6 +6,7 @@ from datetime import datetime, timedelta, timezone
 import json
 from kubernetes import client
 from kubernetes_service import apps_v1, custom_objects_api, k8s_manager, v1
+from namespace_utils import user_namespace
 import random
 import re
 from runtime_config import (
@@ -75,7 +76,7 @@ def change_server_version(server_id: str, user_id: str, new_version: str, java_v
                 logger.info(f"✓ Changed version for server {server_id} to {new_version} (billing date unchanged)")
                 return cursor.rowcount > 0
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
 
         if not k8s_manager.connected:
             # If K8s not connected, just update database
@@ -368,7 +369,7 @@ def reinstall_server(server_id: str, user_id: str) -> bool:
             if not owner:
                 raise Exception("Server owner not found")
 
-        namespace = f"user-{owner['username']}".lower()
+        namespace = server.get('namespace') or user_namespace(owner['username'])
 
         if not k8s_manager.connected:
             update_server_status(server_id, 'Running')
@@ -1949,7 +1950,7 @@ def create_server(config: Dict, user_id: str, progress_callback=None) -> Dict:
                 'ip': NODE_IP,
                 'ports': ports,
                 'ownerId': user_id,
-                'namespace': f"user-{user['username']}".lower(),
+                'namespace': user_namespace(user['username']),
                 'k8s_name': server_id,
                 'is_demo': is_demo,
                 'demo_expires_at': demo_expires_at,
@@ -1964,7 +1965,7 @@ def create_server(config: Dict, user_id: str, progress_callback=None) -> Dict:
             server = create_server_record(server_data)
 
         else:
-            namespace = f"user-{user['username']}".lower()
+            namespace = user_namespace(user['username'])
             sanitized_name = config['name'].lower().replace(' ', '-').replace('_', '-')[:20]
             server_id = f"{sanitized_name}-{str(uuid.uuid4())[:8]}"
 
diff --git a/server_records.py b/server_records.py
index f973003..5cd7345 100644
--- a/server_records.py
+++ b/server_records.py
@@ -2,6 +2,7 @@
 
 
 from database_service import database_connection, dict_from_row
+from namespace_utils import user_namespace
 import json
 from runtime_config import (
     logger,
@@ -116,7 +117,7 @@ def get_server_access_and_namespace(server_id: str, requester_id: str) -> Tuple[
     if not owner:
         raise Exception("Server owner not found")
 
-    namespace = f"user-{owner['username']}".lower()
+    namespace = server.get('namespace') or user_namespace(owner['username'])
     return namespace, server
 
 def get_user_servers(user_id: str) -> List[Dict]:
diff --git a/websocket_service.py b/websocket_service.py
index a3cbda3..9aa065a 100644
--- a/websocket_service.py
+++ b/websocket_service.py
@@ -13,6 +13,7 @@ from kubernetes import client
 from kubernetes.client.rest import ApiException
 from kubernetes.stream import stream
 from kubernetes_service import custom_objects_api, k8s_manager, v1
+from namespace_utils import user_namespace
 import os
 import paramiko
 import pyotp
@@ -1263,7 +1264,7 @@ async def handle_register(client_id, data):
 
     if k8s_manager.connected:
         try:
-            k8s_manager.create_namespace(f"user-{username}".lower())
+            k8s_manager.create_namespace(user_namespace(username))
         except Exception:
             pass
 
@@ -2051,7 +2052,7 @@ async def handle_upload_file(client_id, data):
             })
             return
 
-        namespace = f"user-{user['username']}".lower()
+        namespace = user_namespace(user['username'])
         pods = k8s_manager.get_pods_for_server(namespace, server_id)
 
         if not pods:
@@ -3776,7 +3777,7 @@ async def handle_delete_custom_domain(client_id, data):
 
             # If domain was linked to a server, delete IngressRoute
             if domain.get('server_id'):
-                namespace = f"user-{username}".lower()
+                namespace = user_namespace(username)
                 # Extract subdomain for IngressRoute name
                 domain_name = domain['domain']
                 subdomain = domain_name.split('.')[0] if '.' in domain_name else domain_name