When sending an email to someone in Outlook it remembers their address, so if you try and send another email to them it'll prompt you with it - even if you haven't added them to the address book.
Is there any way of exporting those remembered addresses, or saving them to the address book?
Utilities not really necessary, it is simply a single file See this explanation for details
You only need to know the user name and the name of the associated pst file.
Ahh, since asking the question I've found they're referred to as auto-complete nicknames, and a number of utilities exist for migrating:
