rather than trusting the application you have menetioned, lets investigate for ourselves.
Please open up a command prompt and enter the following command:
netstat -aon | find ":25"
Once this has been done look for lines which contain :25 if any exist the application is correct and we need to look more closly at the software running on the box. If not the software is not accurate.
Now you have checked and found a line showing port 25 is infact open on your machine, we need to see what that process is.
tasklist | find "1856"
This command lists all running tasks on your computer and with the "find" pipeline it can limit the results to the process ID you showed me in your comment.
Bear in mind!
One thing you need to bear in mind is that your server unless it is on a DMZ/Connectect directly to the internet or has a NAT port forward on your Firewall/Router is invisible to the internet.
Dave on the comment of your post has the right idea to test this. If you attempt this from home or any network with access to the internet which isnt your own.
Open a command prompt and type the below:
telnet <externalIPaddress> 25
If you get a banner page make a note of what message you are displayed as this will help us identify which server is setup to recieve port 25 from your Firewall/Router.
Please Note this answer is being updated as more information is being provided