When we type an email address in Outlook to send an email, Autocomplete feature provides a list of Recent People and Suggestions in the drop down list.The latest update provides up to 5 suggestions. If you want to delete an email ID from other suggestions list then there is no X sign next to it and you will not be able to remove the entry,
If you like the Old Autocomplete format which display’s full list then you can use below registry entry on client PC.
Close the Re-open the Outlook to get this affected – No restart or Logoff / Login of the PC will be needed.
Once you set the above registry key it will show the autocomplete entries like below: