Sets ImmutableIDs for all Office 365 users based on AD...without needing to touch anything.

FixOffice365Users.ps1

function Get-ImmutableId ($a) {
  [System.Convert]::ToBase64String(([guid](Get-ADUser $a -Properties ObjectGuid).ObjectGuid).ToByteArray())
}

##
## WARNING: This script does not health check anything at all. 
##          If you run it without knowing what it does, you 
##          will probably break the internet, and not in the good way.
##

Get-MsolUser -All | 
  Where {$_.UserPrincipalName -ilike "*@contoso.com" -and $_.ImmutableId -eq $null} | 
  % { $_ | Set-MsolUser -ImmutableId (Get-ImmutableId $b) }

This script doesn't even work, where does $b come from?