Fix datetime serialization in config.py with UTC timezone and ISO format

Author: bonashen

mcp_email_server/config.py

@@ -5,7 +5,7 @@
 from pathlib import Path
 
 import tomli_w
-from pydantic import BaseModel, Field, model_validator
+from pydantic import BaseModel, ConfigDict, Field, model_validator, field_serializer
 from pydantic_settings import (
     BaseSettings,
     PydanticBaseSettingsSource,
@@ -33,6 +33,11 @@ def masked(self) -> EmailServer:
 
 
 class AccountAttributes(BaseModel):
+    model_config = ConfigDict(
+        json_encoders={
+            datetime.datetime: lambda v: v.isoformat()
+        }
+    )
     account_name: str
     description: str = ""
     created_at: datetime.datetime = Field(default_factory=datetime.datetime.now)
@@ -59,6 +64,10 @@ def __eq__(self, other: object) -> bool:
             exclude={"created_at", "updated_at"}
         )
 
+    @field_serializer('created_at', 'updated_at')
+    def serialize_datetime(self, v: datetime.datetime) -> str:
+        return v.isoformat()
+
     def masked(self) -> AccountAttributes:
         return self.model_copy()