Implement validation for RFC 5536 mandatory headers

lib/nntp/tiny/message.py

@@ -355,6 +355,25 @@ class Message(DatabaseTable):
                 remote
             )
 
+    def validate(self):
+        if self.created_on is None:
+            return False
+
+        if self.sender is None:
+            return False
+
+        if self.message_id is None:
+            return False
+
+        if self.subject is None:
+            return False
+
+        if self.header('Newsgroups') is None:
+            return False
+
+        if self.header('Path') is None:
+            return False
+
     @staticmethod
     def from_text(text: str):
         message = Message()