Why can I only add a note to this conversation and not an email reply?

Occasionally, you may click the Reply link on a conversation and end up on the 'Notes' panel instead. 

This is usually a sign that the brand to which the conversation belongs doesn't have an email address setup for it yet. Once you've added an address for that brand, you'll be able to reply to the conversation like normal.

For help, check out our user guide article about adding email accounts to your Kayako.