If you ever encounter a situation that you need to send A warning message to all users unprecedented this is a good quick trick!
( Import module activedirecory is required for this )
Code:
(Get-ADComputer -Filter *).name | ForEach-Object {msg “*” /Server:$_ “**IMPORTANT NOTICE FROM IT *** Following on from the email sent earlier, please save your work and reboot your PC to allow us to resolve the issue”}