check if certain ports can be reached from your internal network or if they are blocked

Test-Ports.ps1

# check if certain ports can be reached from your internal network or if they are blocked

# note: adapted from https://github.com/JustinGrote/Scripts/blob/master/Test-TCPPort.ps1
function Test-Port()
{
    Param([string]$srv, $port = 135, $timeoutMs = 3000, [switch]$verbose)

    $failed = $false
    $ErrorActionPreference = "SilentlyContinue"
    $tcpclient = New-Object System.Net.Sockets.TcpClient
    $asyncRes = $tcpclient.BeginConnect($srv,$port,$null,$null)

    # wait for the specified number of milliseconds
    $wait = $asyncRes.AsyncWaitHandle.WaitOne($timeoutMs, $false)

    # check for timeout
    if(!$wait)
    {
        # close the connection and report timeout
        $tcpclient.Close()
        if ($verbose)
        {
            Write-Host "Connection Timeout"
        }
        $failed = $true
    }
    else
    {
        # close the connection and report the error if there is one
        $Error.Clear()
        $tcpclient.EndConnect($asyncRes) | Out-Null
        if(!$?)
        {
            if($verbose)
            {
                Write-Host $Error[0]
            }
            $failed = $true
        }
        $tcpclient.Close()
    }

    return !$failed
}

$openPorts = @()
$mailPorts = 25,110,465,587,995
foreach ($port in $mailPorts) 
{
    $result = Test-Port portquiz.net -port $port -timeoutMs 500
    if ($result)
    {
        Write-Host "Port is open: $port" -ForegroundColor Green
        $openPorts += $port
    } else {
        Write-Host "Port is closed: $port" -ForegroundColor Red
    }
}

Write-Host "Detected open ports:"
$openPorts