Skip to main content

Doing a SMTP telnet test with a Powershell script

One of the array of diagnostic tests you may find yourself doing when you’re trying to fix a problem sending and receiving messages to a domain is to do a telnet on Port 25 to a mail server you maybe having a problem with and then trying to run though manually issuing the SMTP commands to send a message to this server so you can see what the responses are. A description of this process can be found in this KB there is also a great tool called SMTPDiag which will run this type of test and more. If you want to do the same thing from a Powershell script well your in luck because the .Net framework makes this process pretty easy. Lee Holmes posted this great script for replacing the missing Telnet on Vista. What I’ve done is rework this script so instead of being an interactive telnet script it’s a script that connects to port 25 on a mail server and then runs through issuing Mail FROM and RCPT TO commands and shows the responses back to the command-line. The script itself takes three command line parameters which are the DNS or IP of the server you want to test and a domainname for the domain you want to test to see if the server will receive email for and a domainname to test a send from( The script doesn’t actually send a message as it quits after the RCPT TO command). To run the script you need to use something like

C:\tnetsmtp.ps1 server.com.au recipeintdomain.com sendingdomain.com

(9/10/2006 Updated input parameters thanks to Hector)

I’ve put a downloadable copy of the code here the script itself looks like.

#param([String] $remoteHost =$(throw "Please specify the Target Server"),[String] $domain = $(throw "Please specify the #recipient Domain"),[String] $sendingdomain = $(throw "Please specify the Sending Domain"))

param([String] $remoteHost,[String] $domain, [String] $sendingdomain)


if ($remotehost -eq "" -or $domain -eq "" -or $sendingdomain -eq "") {"Please specify the Target Server, recipient domain and sending domain"
return; }


function readResponse {

while($stream.DataAvailable)
{
$read = $stream.Read($buffer, 0, 1024)
write-host -n -foregroundcolor cyan ($encoding.GetString($buffer, 0, $read))
""
}
}

$port = 25
$socket = new-object System.Net.Sockets.TcpClient($remoteHost, $port)
if($socket -eq $null) { return; }

$stream = $socket.GetStream()
$writer = new-object System.IO.StreamWriter($stream)
$buffer = new-object System.Byte[] 1024
$encoding = new-object System.Text.AsciiEncoding
readResponse($stream)
$command = "HELO "+ $domain
write-host -foregroundcolor DarkGreen $command
""
$writer.WriteLine($command)
$writer.Flush()
start-sleep -m 500
readResponse($stream)
$command = "MAIL FROM: "
write-host -foregroundcolor DarkGreen $command
""
$writer.WriteLine($command)
$writer.Flush()
start-sleep -m 500
readResponse($stream)
$command = "RCPT TO: "
write-host -foregroundcolor DarkGreen $command
""
$writer.WriteLine($command)
$writer.Flush()
start-sleep -m 500
readResponse($stream)
$command = "QUIT"
write-host -foregroundcolor DarkGreen $command
""
$writer.WriteLine($command)
$writer.Flush()
start-sleep -m 500
readResponse($stream)
## Close the streams
$writer.Close()
$stream.Close()

Popular posts from this blog

The MailboxConcurrency limit and using Batching in the Microsoft Graph API

If your getting an error such as Application is over its MailboxConcurrency limit while using the Microsoft Graph API this post may help you understand why. Background   The Mailbox  concurrency limit when your using the Graph API is 4 as per https://docs.microsoft.com/en-us/graph/throttling#outlook-service-limits . This is evaluated for each app ID and mailbox combination so this means you can have different apps running under the same credentials and the poor behavior of one won't cause the other to be throttled. If you compared that to EWS you could have up to 27 concurrent connections but they are shared across all apps on a first come first served basis. Batching Batching in the Graph API is a way of combining multiple requests into a single HTTP request. Batching in the Exchange Mail API's EWS and MAPI has been around for a long time and its common, for email Apps to process large numbers of smaller items for a variety of reasons.  Batching in the Gr...
Read more

Sending a MimeMessage via the Microsoft Graph using the Graph SDK, MimeKit and MSAL

One of the new features added to the Microsoft Graph recently was the ability to create and send Mime Messages (you have been able to get Message as Mime for a while). This is useful in a number of different scenarios especially when trying to create a Message with inline Images which has historically been hard to do with both the Graph and EWS (if you don't use MIME). It also opens up using SMIME for encryption and a more easy migration path for sending using SMTP in some apps. MimeKit is a great open source library for parsing and creating MIME messages so it offers a really easy solution for tackling this issue. The current documentation on Send message via MIME lacks any real sample so I've put together a quick console app that use MSAL, MIME kit and the Graph SDK to send a Message via MIME. As the current Graph SDK also doesn't support sending via MIME either there is a workaround for this in the future my guess is this will be supported.
Read more

EWS-FAI Module for browsing and updating Exchange Folder Associated Items from PowerShell

Folder Associated Items are hidden Items in Exchange Mailbox folders that are commonly used to hold configuration settings for various Mailbox Clients and services that use Mailboxes. Some common examples of FAI's are Categories,OWA Signatures and WorkHours there is some more detailed documentation in the https://msdn.microsoft.com/en-us/library/cc463899(v=exchg.80).aspx protocol document. In EWS these configuration items can be accessed via the UserConfiguration operation https://msdn.microsoft.com/en-us/library/office/dd899439(v=exchg.150).aspx which will give you access to either the RoamingDictionary, XMLStream or BinaryStream data properties that holds the configuration depending on what type of FAI data is being stored. I've written a number of scripts over the years that target particular FAI's (eg this one that reads the workhours  http://gsexdev.blogspot.com.au/2015/11/finding-timezone-being-used-in-mailbox.html is a good example ) but I didn't have a gene...
Read more
All sample scripts and source code is provided by for illustrative purposes only. All examples are untested in different environments and therefore, I cannot guarantee or imply reliability, serviceability, or function of these programs.

All code contained herein is provided to you "AS IS" without any warranties of any kind. The implied warranties of non-infringement, merchantability and fitness for a particular purpose are expressly disclaimed.