How to do this in an older version of Outlook?

You need to check and see if Autocomplete is turned off.

From the main outlook page select Tools from the menu bar.
Click options
Select email options
Select advanced email options
Near the bottom of the list of options is a field called “Suggest names while completing To, CC and Bcc. Make sure this box is checked.

Let me know if that was the problem.

No, that’s not it; the box is checked, but hitting ‘enter’ doesn’t put anything in.

OK. It appears your NK2 file may be corrupted. There is a way to fix this. It takes some patience and a number of steps.

http://repair-outlook-autocomplete.blogspot.com/

Read through this at least twice before you begin. You need to decide if you want to do this or call a service like geek squad to do it for you.

Thanks, @Wealthadvisor. I’m not sure I’m that annoyed by it not working:-) But I’m going to save the link. My son used to work in geek squad, maybe I’ll see if I can get him to do it for me, next time he visits.

Update: I have just realized that the problem was not with Outlook… it was because the default email editor was set to Word. Now that I’ve changed that, it works fine. I only found out because one day Word didn’t want to play, for some reason…