Tools / Port checker / 110
Is port 110 open?
Port 110 is POP3. Enter your server below to test it from Dallas, Amsterdam and London.
What port 110 is used for
Post Office Protocol: mail clients download messages from the server.
Should port 110 be open?
Open it only to the addresses that need it. Plain text unless upgraded with STARTTLS. Prefer POP3S on port 995 or IMAPS on 993.
How to open port 110
Ubuntu or Debian with ufw, allowing only your own address (replace 203.0.113.10):
sudo ufw allow from 203.0.113.10 to any port 110 proto tcp
Rocky, Alma or CentOS with firewalld:
sudo firewall-cmd --permanent --add-port=110/tcp && sudo firewall-cmd --reload
Windows Server, in PowerShell as administrator:
New-NetFirewallRule -DisplayName "Port 110" -Direction Inbound -Protocol TCP -LocalPort 110 -Action Allow
Then check that the service listens on all addresses, not only 127.0.0.1, and test again above.
Check another port
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Run your service on a PrivateByte server: a firewall you control and every port yours to open.