After I created a new Outlook profile the auto-complete list is empty. I used to type three letters and the address appeared. Can I restore the old list?

The suggestions come from a file in your profile called the auto-complete cache, not from the contacts folder.

First check the setting. File > Options > Mail > Send messages and make sure "Use Auto-Complete List to suggest names when typing in the To, Cc and Bcc lines" is ticked.

To bring the old list back, close Outlook and look in %localappdata%\Microsoft\Outlook\RoamCache. You will find files named Stream_Autocomplete followed by a long string. Copy the newest one from the old profile into the new profile's matching file name, replacing it, then open Outlook.

If you have no old file, the list rebuilds itself as you send mail. To speed that up, add people to your Contacts folder.

The RoamCache trick worked. The old list is back. I did not know that folder existed.