$LoadRunnerAccounts=Get-ADUser -Filter { Name -like "Loadrunner*" } | select -First 2000
$cred = Get-Credential
foreach ($LoadRunner in $LoadRunnerAccounts) {
    
    Write-Output "Fixing $($LoadRunner.SamAccountName)"
    $MailAddress = $null
    $MailAddress = "$($LoadRunner.SamAccountName)@domain.com"
    $proxyaddresses = "SMTP:$mailaddress","smtp:$($LoadRunner.SamAccountName)@mydomain.onmicrosoft.com"
    Set-ADUser -Identity $LoadRunner -UserPrincipalName $MailAddress -EmailAddress $MailAddress -Replace @{'extensionAttribute4' = "O365Ready" ; 'proxyaddresses' = $proxyaddresses } -Server 'dc01.mydomain.com' -Credential $cred
}