posting replies questions

why are replies to posts often disallowed with the statement: “You have reached your maximum message level”? Are posts messages? where can the rules governing forums be found? Are debating rules of any sort in play? can the name of the poster a reply is being made to, be displayed with the post in the notice email or, alternatively, can the link in this notice email take one directly to the thread tree so the reponse can be related directly to the preceding post?