[SalesForce] Live Agent Post Chat Page

Assuming you already stored the email in the Live Chat Transcript, all you would need to do is to create a workflow rule on that object to send an email to that email address.

It seems like you are trying to call the chat window page directly, this is not allowed.

You need to create a custom chat window page as per the instructions in the Live Agent Developer guide, once you have created that page, go to:

Setup > Live Agent > Chat Buttons > Yourbutton (Edit) > Custom Chat Page (Select your new page here) > Save

Then launch the start as usual using the button code.

Sample Page:

<apex:page showHeader="false">
<style>
body { overflow: hidden; width: 100%; height: 100%; padding: 0; margin: 0 }
#waitingMessage { height: 100%; width: 100%; vertical-align: middle; text-align: center; display: none; }
#liveAgentClientChat.liveAgentStateWaiting #waitingMessage { display: table; }
#liveAgentSaveButton, #liveAgentEndButton { z-index: 2; }
.liveAgentChatInput {
    height: 25px;
    border-width: 1px;
    border-style: solid;
    border-color: #000;
    padding: 2px 0 2px 4px;
    background: #fff;
    display: block;
    width: 99%;
}
.liveAgentSendButton {
    display: block;
    width: 60px;
    height: 31px;
    padding: 0 0 3px;
    position: absolute;
    top: 0;
    right: -67px;
}
#liveAgentChatLog {
    width: auto;
    height: auto;
    top: 0px;
    position: absolute;
    overflow-y: auto;
    left: 0;
    right: 0;
    bottom: 0;
}
</style>
<div style="top: 0; left: 0; right: 0; bottom: 0; position: absolute;">
<liveAgent:clientchat >
    <liveAgent:clientChatSaveButton label="Save Chat" />
    <liveAgent:clientChatEndButton label="End Chat" />
    <div style="top: 25px; left: 5px; right: 5px; bottom: 5px; position: absolute; z-index: 0;">
    <liveAgent:clientChatAlertMessage />
    <liveAgent:clientChatStatusMessage />
    <table id="waitingMessage" cellpadding="0" cellspacing="0">
    <tr>
    <td>Please wait while you are connected to an available agent.</td>
    </tr>
    </table>
    <div style="top: 0; right: 0; bottom: 41px; left: 0; padding: 0; position: absolute; word-wrap: break-word; z-index: 0;">
    <liveAgent:clientChatLog />
    </div>
    <div style="position: absolute; height: auto; right: 0; bottom: 0; left: 0; margin-right: 67px;">
        <liveagent:clientChatInput /><liveAgent:clientChatSendButton label="Send"/>
    </div>
    </div>
</liveAgent:clientchat>
</div>
</apex:page>