Dummy SMTP server and Outlook

[fog37]

TL;DR Summary

Outlook outgoing mail stuck...using dummy smtp mail server

Hello,
I have downloaded the dummy mail server hmailserver because my Outlook is trying to send a couple of emails out but they are stuck. I read that using a dummy smtp server, instead of the actual smtp server, would help get those email out and "reset" Outlook.

I tried but Outlook was not able to connect to this dummy server even if I disabled authentication, used localhost, and used the same port...

Any suggestion?
Thank you!

 

[jbriggs444]

TL;DR Summary: Outlook outgoing mail stuck...using dummy smtp mail server

Hello,
I have downloaded the dummy mail server hmailserver because my Outlook is trying to send a couple of emails out but they are stuck. I read that using a dummy smtp server, instead of the actual smtp server, would help get those email out and "reset" Outlook.

I tried but Outlook was not able to connect to this dummy server even if I disabled authentication, used localhost, and used the same port...

This is in a corporate environment with anti-virus deployed to the desktops?

I've been retired from the I.T. world for almost two years now. But when I was working, the number 1 problem with trying to do SMTP was port blocking rules in the anti-virus software.

So your first step should be to right click on the anti-virus icon and see what control you can exert over it.

If it is not the anti-virus, I would next check on the local server to see whether the dummy smtp server is actually listening on port 25 (vanilla SMTP) and port 587 (SMTP with TLS). My normal approach for this is to get out to a command prompt. At the C:\> prompt, key in "netstat -na". e.g.

C:\Users\John>netstat -na

Active Connections

  Proto  Local Address          Foreign Address        State
  TCP    0.0.0.0:135            0.0.0.0:0              LISTENING
  TCP    0.0.0.0:445            0.0.0.0:0              LISTENING
  TCP    0.0.0.0:5040           0.0.0.0:0              LISTENING
  TCP    0.0.0.0:5357           0.0.0.0:0              LISTENING

You are looking for TCP on the 0.0.0.0 address with a ":25" or ":587".

In the example above, I am not listening for SMTP. I am listening for RPC and SMB on ports 135 and 445.

If this shows that your machine is not listening on port 25, then the problem is with your dummy SMTP server.

If you are listening on port 25, then the next thing that I would do is to attempt a TCP connection to port 25 and see whether it connects.

In the old days when "telnet" came pre-installed on Windows, this was easy. C:\> telnet localhost 25

Microsoft, in their infinite wisdom, stopped shipping telnet. But they still ship FTP. One can leverage the FTP client to do port testing.

C:\Users\John>ftp
ftp> open localhost 445
Connected to JohnsThor.
Aborting any active data connections...
Connection closed by remote host.
ftp> quit

C:\Users\John>ftp
ftp> open localhost 25
> ftp: connect :Connection refused
ftp>

If you see "Connected", the connection is good.
If you see "Connection refused", you are getting there, but the target is not listening
If you get nothing but a blinking cursor for 30 seconds or more, the port is likely blocked by a filter or firewall.

If you want to dig deeper than this, you could download something like "ncat". This can act as a richly functional telnet client and let you fully check out the dummy SMTP server functionality.

Or you could download Wireshark. This a packet sniffer. I do not think that Wireshark works on the loopback interface. You need to get the packets to flow out your actual Ethernet port. You cannot cheat by using the IP address of your local workstation's Ethernet adapter. The TCP stack knows that one is local and will short circuit your traffic anyway. So you'll need to put the SMTP server on some other box for troubleshooting.

Now, back to where we started...

The reason that anti-virus suites like to block port 25 outbound is to prevent malware from phoning home or from propagating via email. Usually they will have exception rules to let you whitelist individual ports or whitelist particular applications.