Port 143 (TCP) — IMAP

Check if port 143 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':143 '

From another machine, test reachability:

nc -zv your-server.example.com 143

Block port 143 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 143

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=143/tcp && sudo firewall-cmd --reload

← All common ports