$users = Get-ADUser -SearchBase "ou=Company Users,dc=domain,dc=org" -Filter *
foreach ($user in $users) {
$pax = (Get-ADUser -Identity $user -Properties proxyaddresses).proxyaddresses
$firstname = (Get-ADUser -Identity $user -Properties givenname).givenname
$lastname = (Get-ADUser -Identity $user -Properties surname).surname
foreach ($address in $pax) {
    if ($address -cmatch '^x500:.') {
        $x500 = $address
    }
    }
$newList = @()
$newList += "SMTP:$firstname.$lastname@company.org"
$newList += "smtp:$firstname.$lastname@company.onmicrosoft.com"
Set-ADUser -Identity $user -Clear proxyaddresses
foreach ($address in $newList) {
Set-ADUser -Identity $user -Add @{
        'proxyAddresses' = $address
}
    }
    Set-ADUser -Identity $user -Add @{
        'proxyAddresses' = $x500
}
}