Whenever a player opens a message, the whole conversation is retrieved and showed to the user.
This way to satisfy user's request may be simple and efficient as long as the conversation is made of few messages and it is between two people; however, when recipients increase in number (and messages in conversations as well), all conversation messages are still retrieved and showed to user: by doing so, overhead is added to user's client and it takes some seconds to show the whole conversation.
As a side effect, sometimes CAPTCHAs retrieval times out and is not showed even if required.
The simplest and most immediate solution to these issues is splitting the conversation into pages like it were a bulletin board topic like the one we're using right now.