diff --git a/api/configs/feature/__init__.py b/api/configs/feature/__init__.py
index ffd5838279..3813c7696e 100644
--- a/api/configs/feature/__init__.py
+++ b/api/configs/feature/__init__.py
@@ -797,12 +797,12 @@ class MailConfig(BaseSettings):
     )
 
     # Microsoft OAuth 2.0 configuration for SMTP
-    MICROSOFT_OAUTH2_CLIENT_ID: Optional[str] = Field(
+    MICROSOFT_OAUTH2_CLIENT_ID: str | None = Field(
         description="Microsoft OAuth 2.0 client ID for SMTP authentication",
         default=None,
     )
 
-    MICROSOFT_OAUTH2_CLIENT_SECRET: Optional[str] = Field(
+    MICROSOFT_OAUTH2_CLIENT_SECRET: str | None = Field(
         description="Microsoft OAuth 2.0 client secret for SMTP authentication",
         default=None,
     )
@@ -812,7 +812,7 @@ class MailConfig(BaseSettings):
         default="common",
     )
 
-    MICROSOFT_OAUTH2_ACCESS_TOKEN: Optional[str] = Field(
+    MICROSOFT_OAUTH2_ACCESS_TOKEN: str | None = Field(
         description="Microsoft OAuth 2.0 access token for SMTP authentication",
         default=None,
     )
diff --git a/api/extensions/ext_mail.py b/api/extensions/ext_mail.py
index d23710483a..19c728eb5e 100644
--- a/api/extensions/ext_mail.py
+++ b/api/extensions/ext_mail.py
@@ -83,7 +83,7 @@ class Mail:
             case _:
                 raise ValueError(f"Unsupported mail type {mail_type}")
 
-    def _get_oauth_token(self) -> Optional[str]:
+    def _get_oauth_token(self) -> str | None:
         """Get OAuth access token using client credentials flow"""
         try:
             from libs.mail.oauth_email import MicrosoftEmailOAuth
@@ -110,7 +110,7 @@ class Mail:
             logging.warning("Failed to obtain OAuth 2.0 access token: %s", str(e))
             return None
 
-    def send(self, to: str, subject: str, html: str, from_: Optional[str] = None):
+    def send(self, to: str, subject: str, html: str, from_: str | None = None):
         if not self._client:
             raise ValueError("Mail client is not initialized")
 
diff --git a/api/libs/mail/oauth_email.py b/api/libs/mail/oauth_email.py
index 0ece9aa865..2fbdcd1a49 100644
--- a/api/libs/mail/oauth_email.py
+++ b/api/libs/mail/oauth_email.py
@@ -23,7 +23,7 @@ class EmailOAuth:
         client_id: str,
         client_secret: str,
         redirect_uri: str,
-        http_client: Optional[OAuthHTTPClientProtocol] = None,
+        http_client: OAuthHTTPClientProtocol | None = None,
     ):
         self.client_id = client_id
         self.client_secret = client_secret
@@ -67,12 +67,12 @@ class MicrosoftEmailOAuth(EmailOAuth):
         client_secret: str,
         redirect_uri: str,
         tenant_id: str = "common",
-        http_client: Optional[OAuthHTTPClientProtocol] = None,
+        http_client: OAuthHTTPClientProtocol | None = None,
     ):
         super().__init__(client_id, client_secret, redirect_uri, http_client)
         self.tenant_id = tenant_id
 
-    def get_authorization_url(self, invite_token: Optional[str] = None) -> str:
+    def get_authorization_url(self, invite_token: str | None = None) -> str:
         """Generate OAuth authorization URL"""
         params = {
             "client_id": self.client_id,
diff --git a/api/libs/mail/oauth_http_client.py b/api/libs/mail/oauth_http_client.py
index d23dd04e90..3c1b7ebf9b 100644
--- a/api/libs/mail/oauth_http_client.py
+++ b/api/libs/mail/oauth_http_client.py
@@ -11,13 +11,13 @@ class OAuthHTTPClientProtocol(ABC):
 
     @abstractmethod
     def post(
-        self, url: str, data: dict[str, Union[str, int]], headers: Optional[dict[str, str]] = None
+        self, url: str, data: dict[str, Union[str, int]], headers: dict[str, str] | None = None
     ) -> dict[str, Union[str, int, dict, list]]:
         """Make a POST request"""
         pass
 
     @abstractmethod
-    def get(self, url: str, headers: Optional[dict[str, str]] = None) -> dict[str, Union[str, int, dict, list]]:
+    def get(self, url: str, headers: dict[str, str] | None = None) -> dict[str, Union[str, int, dict, list]]:
         """Make a GET request"""
         pass
 
@@ -26,7 +26,7 @@ class OAuthHTTPClient(OAuthHTTPClientProtocol):
     """Default implementation using requests library"""
 
     def post(
-        self, url: str, data: dict[str, Union[str, int]], headers: Optional[dict[str, str]] = None
+        self, url: str, data: dict[str, Union[str, int]], headers: dict[str, str] | None = None
     ) -> dict[str, Union[str, int, dict, list]]:
         """Make a POST request"""
         response = requests.post(url, data=data, headers=headers or {})
@@ -37,7 +37,7 @@ class OAuthHTTPClient(OAuthHTTPClientProtocol):
             "headers": dict(response.headers),
         }
 
-    def get(self, url: str, headers: Optional[dict[str, str]] = None) -> dict[str, Union[str, int, dict, list]]:
+    def get(self, url: str, headers: dict[str, str] | None = None) -> dict[str, Union[str, int, dict, list]]:
         """Make a GET request"""
         response = requests.get(url, headers=headers or {})
         response.raise_for_status()
diff --git a/api/libs/mail/smtp.py b/api/libs/mail/smtp.py
index 7410bac162..f75562ef05 100644
--- a/api/libs/mail/smtp.py
+++ b/api/libs/mail/smtp.py
@@ -83,12 +83,12 @@ class SMTPClient:
         from_addr: str,
         use_tls: bool = False,
         opportunistic_tls: bool = False,
-        oauth_access_token: Optional[str] = None,
+        oauth_access_token: str | None = None,
         auth_type: str = "basic",
-        connection_factory: Optional[SMTPConnectionFactory] = None,
-        ssl_connection_factory: Optional[SMTPConnectionFactory] = None,
-        authenticator: Optional[SMTPAuthenticator] = None,
-        message_builder: Optional[SMTPMessageBuilder] = None,
+        connection_factory: SMTPConnectionFactory | None = None,
+        ssl_connection_factory: SMTPConnectionFactory | None = None,
+        authenticator: SMTPAuthenticator | None = None,
+        message_builder: SMTPMessageBuilder | None = None,
     ):
         self.server = server
         self.port = port
diff --git a/api/tests/unit_tests/libs/mail/test_oauth_email.py b/api/tests/unit_tests/libs/mail/test_oauth_email.py
index b502d0a3de..26a1b808fb 100644
--- a/api/tests/unit_tests/libs/mail/test_oauth_email.py
+++ b/api/tests/unit_tests/libs/mail/test_oauth_email.py
@@ -36,7 +36,7 @@ class MockHTTPClient(OAuthHTTPClientProtocol):
         self.get_responses.append(json_data)
 
     def post(
-        self, url: str, data: dict[str, Union[str, int]], headers: Optional[dict[str, str]] = None
+        self, url: str, data: dict[str, Union[str, int]], headers: dict[str, str] | None = None
     ) -> dict[str, Union[str, int, dict, list]]:
         """Mock POST request"""
         self.post_calls.append({"url": url, "data": data, "headers": headers})
@@ -54,7 +54,7 @@ class MockHTTPClient(OAuthHTTPClientProtocol):
             "headers": {},
         }
 
-    def get(self, url: str, headers: Optional[dict[str, str]] = None) -> dict[str, Union[str, int, dict, list]]:
+    def get(self, url: str, headers: dict[str, str] | None = None) -> dict[str, Union[str, int, dict, list]]:
         """Mock GET request"""
         self.get_calls.append({"url": url, "headers": headers})
 
diff --git a/api/tests/unit_tests/libs/test_smtp_client.py b/api/tests/unit_tests/libs/test_smtp_client.py
index fcee01ca00..7e9f194e5f 100644
--- a/api/tests/unit_tests/libs/test_smtp_client.py
+++ b/api/tests/unit_tests/libs/test_smtp_client.py
@@ -1,7 +1,6 @@
 from unittest.mock import MagicMock, patch
 
 import pytest
-
 from libs.smtp import SMTPClient