Quick one-liner for setting UPNs for users to match their email address (useful for working with Azure, O365, etc.)

UPN.ps1

#Set UPN for all users with mobile phone numbers to email address
Get-ADuser -Filter * -Properties mobilephone, mail | where {$_.mobilephone -and $_.mail -ne $_.userPrincipalName} | ForEach-Object {Set-ADuser -Identity $_.ObjectGUID -UserPrincipalName $_.mail}

#Set UPN for all users to email address
Get-ADuser -Filter * -Properties mail | where {$_.mail -ne $_.userPrincipalName} | ForEach-Object {Set-ADuser -Identity $_.ObjectGUID -UserPrincipalName $_.mail}