Invoke-Command Exchange

If ($ForwardEmailTo -ne $NULL) {
    $ExchangeServer = 'ServerName'
    $Block = {
        Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn
        Set-Mailbox $args[0] -forwardingaddress $args[1]
    }
    Write-Warning "Forwarding $UserName emails to $ForwardEmailTo"
    Invoke-Command -Session (New-PSSession -ComputerName $ExchangeServer -Authentication Kerberos) -ScriptBlock $Block -ArgumentList $UserName,$ForwardEmailTo
    Get-PSSession | Remove-PSSession
    Write-Verbose "Emails sent to $UserName are now being forwarded to the following user:"
}
Else {
    Write-Warning "Emails for $UserName are not being forwarded. Check who these need to be forwarded to and set this in the Exchange Console."
}