Using netcat as a server

Just this morning I was checking out some piece of software and was trying to setup its mail configuration. But it would not function the way I thought it was supposed to so I had a look into my mail server logfile. With the tailf -command I would be seeing the messages to and from the mail server. But as I was looking at little to no action the logfile suddenly was filling my screen with messages.

Someone was trying to use my mailserver....


There was a new connection attempt about every 2 seconds and I was getting curious to what this was. I have heard about and used netcat before so I decided to stop the mail server and start listening through netcat.

 By the time I was done figuring out the right command for netcat; the intruder had given up and probably went on to another mailserver. But the next time I will answer with netcat and see if I can find out what exactly this intruder is trying to do. (My guess is that someone wants to use my mailserver for spamming purposes.)

The short command to use with netcat is:

sudo netcat -lv 25

This will listen to port 25 and allow me to respond to whatever the intruder is trying to send to my computer.