Port 110 (TCP) — POP3

Check if port 110 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':110 '

From another machine, test reachability:

nc -zv your-server.example.com 110

Block port 110 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 110

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=110/tcp && sudo firewall-cmd --reload

← All common ports