Port 53 should not be open

Good day,

I was little surprised to find port 53 open when I did an external scan on my server.

I used the following nmap command: sudo nmap -sT -sV mail.example.com

Which gave me the following:

53/tcp open domain ISC BIND 9.11.3-1ubuntu1.13

When I run sudo systemctl status bind9 from the server it says this...

Unit bind9.service could not be found.

What exactly is running on port 53? And according to nftables port 53 should be closed. I didn't install a DNS server so I'm a little confused

Any help would be greatly appreciated.

Thanks