If a problem arises with an email account set up in Microsoft Outlook, it may be necessary to remove and replace account settings or create an entirely new Outlook profile. This will generally empty Outlook’s AutoComplete cache, its ability to predict possible email addresses from your history as you type them in.
Backup and restore Outlook’s old AutoComplete file to replace the new, empty file it creates.
First, close Outlook and verify that no Outlook.exe tasks are running in Windows Task Manager. Next, use File Explorer to navigate to C:\Users\<Username>\AppData\Local\Microsoft\Outlook\RoamCache\ and examine the list of files there. There should be at least two files with names similar to Stream_Autocomplete_*.dat, where the “*” will be replaced by a long string of letters and numbers. These will be the new and old AutoComplete data files, and the larger of the two will likely be the older file containing the required data.
Make backup copies of both Stream_Autocomplete_*.dat files in a separate location where they can be retrieved later if something goes wrong.
Select the smaller, new AutoComplete file, then click it a second time or press F2, as though to rename the file. Select all of the text in the filename, and copy it by right-clicking on it or pressing Ctrl-C.
Delete or rename this file, then rename the larger, older file to match the new file’s name.
The larger, older file should now have the filename of the newer file.
When done, restart Outlook and your AutoComplete list should return.
When examining the C:\Users\<Username>\AppData\Local\Microsoft\Outlook\RoamCache\ folder, an older file may not be present. In this case the AutoComplete list may be unrecoverable.