When troubleshooting SMTP or other service connectivity on Windows Server 2008 R2 systems without Telnet client installed, administrators need reliable native alternatives that don't require additional installations. Here are several practical approaches:

# PowerShell Test-NetConnection alternative (Server 2012+ only)
Test-NetConnection mail.example.com -Port 25

# Legacy PowerShell workaround
$socket = New-Object System.Net.Sockets.TcpClient
try {
    $socket.Connect("mail.example.com", 25)
    if($socket.Connected) {
        Write-Output "Port 25 is open"
        $stream = $socket.GetStream()
        $reader = New-Object System.IO.StreamReader $stream
        Write-Output $reader.ReadLine()
    }
} catch {
    Write-Output "Connection failed: $_"
} finally {
    $socket.Close()
}

• Internet Explorer: Navigate to http://mail.example.com:25. While not ideal, it may show raw SMTP response if the port is open
• FTP Client: Can test FTP ports (21) with ftp> open ftp.example.com 21

For environments where temporary tools are acceptable:

# Download portable PuTTY (no installation required)
bitsadmin /transfer getPuTTY /download /priority high https://the.earth.li/~sgtatham/putty/latest/w64/putty.exe %TEMP%\putty.exe

# Test connection (example for SMTP)
%TEMP%\putty.exe -telnet mail.example.com 25

Create a porttest.vbs file with this code:

Set objArgs = WScript.Arguments
host = objArgs(0)
port = objArgs(1)
Set objTCP = CreateObject("MSWinsock.Winsock")
objTCP.Protocol = 0 'TCP
objTCP.RemotePort = port
objTCP.RemoteHost = host
objTCP.Connect
WScript.Sleep 1000
If objTCP.State = 7 Then
    WScript.Echo "Port " & port & " is open"
Else
    WScript.Echo "Connection failed (State: " & objTCP.State & ")"
End If

Execute with: cscript porttest.vbs mail.example.com 25

When working with Windows Server 2008 systems that lack the telnet client, these built-in tools can help verify port connectivity:

# PowerShell Test-NetConnection (Server 2012+, but works in 2008 with PS 3.0+)
Test-NetConnection mailserver.tld -Port 25

# Classic PowerShell approach
$socket = New-Object System.Net.Sockets.TcpClient
$socket.Connect("mailserver.tld", 25)
$socket.Connected # Returns $true if successful

For HTTP/SMTP services, simply entering the URL in IE can reveal basic connectivity:

http://mailserver.tld:25/

Note: This works best with HTTP-based services, SMTP may return garbled text but confirms the port is open.

While technically requiring download, PortQryUI is a Microsoft-signed tool that's often allowed in locked-down environments:

PortQryUI.exe -n mailserver.tld -e 25 -p TCP

Create a VBS script for port testing:

Set objShell = CreateObject("WScript.Shell")
objShell.Run "cmd /c echo QUIT | nc mailserver.tld 25", 0, True

If you have access to performance monitor:

1. Open perfmon
2. Add TCPv4/Connections Established counter
3. Attempt connection via other method
4. Watch for connection spike

For SMTP specifically, abuse the Windows fax service:

# In PowerShell
$smtp = New-Object System.Net.Mail.SmtpClient("mailserver.tld", 25)
try {
    $smtp.Send("test@local", "admin@domain.com", "Test", "Test body")
    Write-Host "Port 25 responsive"
} catch {
    Write-Host "Connection failed"
}

Remember to document your testing methodology as firewall rules may block some of these techniques while allowing others.