Want to see a list of people you’ve emailed over the last, say, two or three years — in date order? Open Mail app then click Window -> Previous Recipients. In the window that appears, click the Last Used heading.
The list on my computer goes back to 15 July 2011, which is when I bought the computer.
You can also select one entry (or several using the usual Shift/Command clicking) and click the Add to Contacts button, to create an entry in Contacts app using their name and email address. Note that you don’t get the chance to further edit the new card, although if you then double-click the entry in the list you’ll open Contacts with the new card showing.
You could just view your Sent mails to see this info, but if you have more than one account (I have several for Gmail and iCloud) then you’ll have to switch between them to put together a list in your head. This technique is simpler and quicker.