I remember reading a tutorial here on making a honeypot using the python programming language:
python socket program, a basic honeypot
So I decided to post sort of the same thing except with java. I didn't make this a tutorial because it is very basic and it really isn't that good. I started with some programs from a knock knock joke example here:
Then I modified them to listen on port 25 and have different output. The attached files are the "honeypot". To run it compile each, they must be in the same directory. I used jcreator to modify and compile them. Then to start the server run the smtpmulti.java file. It will run until you stop it. It will except all telnet connections at port 25. you can modify what the server will output by changing it in the smtpprotocol.java file and recompiling. Hope this is useful. you can see mine by typing
telnet 25
at the command prompt.