This article describes a simple method to help you understand the process of restoring the AutoComplete feature in Outlook after you perform an upgrade or change Outlook profiles.
Outlook maintains an AutoComplete list. The AutoName Check feature and the AutoComplete feature use this list. The AutoComplete list (also known as the Nickname Cache) is automatically generated when you send email messages from Outlook. The list contains the SMTP addresses, LegacyExchangeDN entries, and display names of people you have previously sent messages to.
Note: The AutoComplete list for Outlook is specific to Outlook and is not shared by Outlook Web App (OWA). OWA maintains its own AutoComplete list.
Then you would want to navigate to (C:\Users\your User profile name\AppData\Local\Microsoft\Outlook\RoamCache) and locate two files named ‘Stream_Autocomplete…..dat‘ and make a copy of them. Then find the newest of the two files from the Date Modified column and copy the file name to clipboard and continue to rename that file with a .old extension on the end and save. Then Right-Click and rename the older of the two files by coping the name of the newer file you have stored on the clipboard and save.
