Sometimes you need to refresh offline address book in Outook, especially when user’s SMIME certificate was refreshed(some other user’s of course) but your outlook keeps the old one even though download of new address book was issued from the menu. Updating Offline Address Book(OAB)  in cached mode can take up to 24 hours no matter how many times you hit “Download Addressbook” button in the menu!

What I found working is one liner, that can be run independently of outook(you can leave it running) but my advice would be to close it.

Open powershell and paste below script:

Get-ChildItem -literalpath "C:\Users\$env:username\AppData\Local\Microsoft\Outlook\Offline Address Books" -recurse -Depth 1 | foreach{Remove-Item $_.FullName -Force -Recurse -ErrorAction SilentlyContinue}

It will delete all offline address books from outlook local app data for current user. Outlook will automatically pull the data from Exchange upon starting.

Now, new certificates will be used and encryption will work again!