There are add ons that will find and add addresses from all your mail. I am not sure how practical adding all incoming email addresses is. Who whats all those junk addresses. It is very simple to add an address from an email when viewing it in a tab or the message pane. There is a star to the right of the senders address. If the star is filled with color it is already in one of your address books. If the star is empty, clicking it adds it to the personal book. Clicking a filled star opens the edit dialog box for that contact so you can select a different book or add details for that contact. This is NOT the same star that is to the left of the message header in the Inbox. Outgoing addresses are added to your Collected book by default.