I encountered this port and found out that it is used for private.
I google it but I still could not figure out what exactly does it mean private mail.
I did find link about service that offer you private email, but not an exact definition of what it mean?
Can someone please explain to me, is there a standard that need to be faced in order to be called private mail?
Normally mail is transferred between mail servers on port 25.
If your system is listening on port 24 you will only be able to send/receive from other servers listening on the same port.
You would probably want to do this locally and have two servers running, one on 25 and one on 24.
Compare to running two web servers, one on port 80 and the other on port 81.
so there is no difference between "private mail" system and mail system but to the fact that they listen to different ports?
Am I right?
Yes that is correct.