If this is not possible consider it a feature request. It would be great if we could set a list of email addresses (or have a checkbox in each address book contact) that would specify which emails to always send receipts to. Communications have various degrees of importance. Some people you communicate with may be related to a specific project, for which you may or may not need return receipts. On top of that, some people are busier than others. Someone may be receiving 10 times more emails per day than someone else. For them it's preferable to make sure the message you sent didn't slip through the cracks or have proof on your side that they received it. But for others, it's overkill, not very eco-friendly and clutters your inbox. Manually specifying whether or not to send a return receipt on every message you send is risky, as you may not always think to do it, and then your important message sits for days or weeks before someone realizes it wasn't read.