It seems that 'edit' and 'delete' both internal notes and replies to customers, have all been lumped together. Allowing agents to edit, or delete replies that have been emailed to a customer, is a terrible idea. One cannot rewrite history. On the other hand, allowing them to edit or delete their own internal notes, makes a lot of sense - even just for typos etc - but more importantly to fix inaccurate info. Permissions should be split such it's possible to only inhibit changes to things sent externally.