Kurt Shintaku's Blog

Because of CA Assembly Bill 1637, many municipal government organizations find themselves needing to change their Top-level domain names from .ORG/.COM to .GOV by January 1, 2029.

In order to plan (or execute) on this order, many county & city IT departments may want to “flush the cache” of their Microsoft Outlook desktop installs, so users no longer type names and obtain the ‘legacy domain-based’ email addresses like user@countyname.ORG & instead resolve to user@countyname.GOV.

Here are some ways to clear/flush the email name resolution cache on managed Outlook installations:

• Remove all addresses from the Auto-Complete list via UI or Command Line
  If you want to reset the Auto-Complete list to remove all addresses at once:  In the Microsoft 365 version of Outlook, the Auto-Complete list is kept in a special hidden message in your mailbox. Resetting the list can be done in the following ways:
  • Button: Empty Auto-Complete List
    Using the “Empty Auto-Complete List” button does exactly what is says. You can find the option here;
    File-> Options-> section Mail-> option group: Send messages-> button: Empty Auto-Complete List
  • Startup switch: cleanautocompletecache
    By starting Outlook with the cleanautocompletecache startup switch you’ll achieve the exact same results as using the button “Empty Auto-Complete List.
    You can execute this switch in the following way (note the space in the command);
    Start-> type; outlook.exe /cleanautocompletecache

• PowerShell script to remove all addresses from the Auto-Complete list
  This script removes the AutoComplete cache files, forcing Outlook to look up addresses in the Global Address List (GAL) instead of the local cache.

# Get the current user’s profile path

$profilePath = [System.Environment]::GetFolderPath(‘LocalApplicationData’)

# Define the path to the AutoComplete cache file

$autoCompletePath = “$profilePath\Microsoft\Outlook\RoamCache”

# Remove the AutoComplete cache files

Remove-Item “$autoCompletePath\Stream_Autocomplete*” -Force

# Restart Outlook

Start-Process “outlook.exe”

(from GitHub – michelderooij/Clear-AutoComplete: Script to clear one or more locations where recipient information is cached.)