Currently the prompt asks "Did you forget to attach?" with "Yes" and "No" buttons. The "No" button is on the right.
There are several issues with this:
- Most times the default button is on the right, and in this case the default is to send anyways
- Users associate the words "Yes" "Confirm" etc with performing an action, and "No" "Cancel" "Abort" with stopping. In this case, it is the opposite.
- Users don't read dialog boxes closely, they click the thing that will make it go away so they can get back to work.
I suggest to avoid the confusing "what does yes/no" conversation, to switch both buttons to be action buttons, and to make the default, on the right, be "Don't send".
This is consistent with, eg, the built-in dialog that asks if you want to use Ctrl+Enter as the shortcut for sending an email: They still use Yes/No, but the No button is on the right, and means don't send.