​Most people don’t manage their inbox effectively. Emails should be treated as a list to do. As you complete a task you can just delete the email.

Your inbox should only contain 'tasks', that are actionable items on your list of things to do. Everything that is in your 'Inbox' (including sub-folders) should only be to-do items.

So do it now, delete all emails you have done. If you want to keep some for reference, move them to a new folder that is not in your inbox.

Figure: All inbox items are tasks

In fact, you could go so far as to say you should not do anything unless you have an email telling you to do it (which is why we send ourselves emails). However, very simple tasks can be requested and replied 'done' via IM.

Read Rules to Better IM.