Updates the UPN of all users in a specified location to match their primary SMTP address

Update-UPNs.ps1

$SearchBase = "DC=MargiesTravel,DC=com"

# Get all the users who have proxyAddresses under the margiestravel.com domain
foreach ($user in (Get-ADUser -SearchBase $SearchBase -LdapFilter '(proxyAddresses=*)')) {
    # Grab the primary SMTP address
    $address = Get-ADUser $user -Properties proxyAddresses | Select -Expand proxyAddresses | Where {$_ -clike "SMTP:*"}
    # Remove the protocol specification from the start of the address
    $newUPN = $address.SubString(5)
    # Update the user with their new UPN
    Set-ADUser $user -UserPrincipalName $newUPN
}