I Agree that Zoho Books is doing a great job when it comes to client satisfaction. But i have seen this in other Accounting Software's. The Option to Accept or Decline an Estimate is placed directly in the Email footer rather than clicking the view Invoice button which directs you to the public portal. The Button that says view Estimate will be replaced 2 Choices Instead, "Accept" or "Decline". When the client clicks accept we get notified via zoho books & when the client Declines, it opens a new tab with the Public Link Portal wherein the client mentions the reason for Declining & again we get notified via zoho Books. Hope this could be done and it would be of much use as mostly clients do not prefer to open multiple tabs to notify their intent.