When I scan my server using nmap
$ sudo nmap -sS IP.ADDR.OF.SRVR, I see a line with
25/tcp open smtp. This is despite the fact that I'm not running postfix, exim or any other kind of mail server on the machine.
I have also tried to block port 25, using IP table rules.
$ sudo iptables -A INPUT -p tcp --destination-port 25 -j DROP
But despite running this and verifying that the iptable rule exists with
$ sudo iptables -L -n -v running nmap still shows the port as being open.
I have also run
$ netstat -tulnp on the server to see what ports are open, and port 25 does not show up in the list there.
Very confused on how to proceed, any help or pointers would be much appreciated.
sudo iptables -nvL - https://pastebin.com/5W9V2rrz
sudo iptables -t nat -nvL - https://pastebin.com/v9ST06uz