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Port 110 (TCP) is the default port for POP3, which mail clients use to download emails from a server. The tool shows you the details and generates firewall commands for the port.
Built by Justin Schuessler
Try the commands on your own VPS, with root access and your own firewall.
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Email · Well-known port · OSI layer 7
Retrieve mail from the server, usually deleting it there. Without TLS, passwords and emails are sent in plain text.
IANA: officially registered as pop3
Firewall commands
Open port
sudo ufw allow 110/tcpFor Ubuntu and Debian. ufw creates the rule for both IPv4 and IPv6. If ufw is disabled, allow SSH first (sudo ufw allow 22/tcp), then enable it with sudo ufw enable, or you'll lock yourself out.
On a ZAP-Hosting VPS with an active network firewall, you also need to allow the port in the Customer Panel.
Port 110 explained
On port 110, an email client downloads new emails from the server via POP3. Unlike IMAP, emails are usually copied to the device and then deleted from the server. That works for a single computer, but not for multiple devices. Without STARTTLS, the connection is unencrypted.
POP3 is one of the oldest protocols for retrieving mail. Its current specification is RFC 1939 from 1996. IANA lists port 110 as “pop3”. RFC 8314 now recommends implicit TLS on port 995 for POP3.
Without encryption, port 110 transmits usernames, passwords and emails in plain text. Prefer port 995 with implicit TLS. If you must continue offering port 110, require STARTTLS before login. If you don't need POP3 at all, keep port 110 closed and disable the service.
More ports
These ports are often part of the same setup. Click one to see its explanation and firewall commands.
View all well-known ports and the complete IANA list
Port list source: IANA Service Name and Transport Protocol Port Number Registry, as of October 22, 2026. iana.org
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FAQ
Quick answers about port 110.
Both use POP3. Port 110 starts unencrypted; port 995 is encrypted with TLS from the start. Always use port 995 for new setups.
IMAP is better for most users because it keeps mail consistent across devices. POP3 is only useful if you specifically want to store mail on a single computer. Many mail providers still support it.
By default, POP3 downloads emails and then deletes them from the server. Most email clients let you keep a copy on the server, but nothing is synchronized.
With ufw, sudo ufw allow 110/tcp is enough. With firewalld, run sudo firewall-cmd --permanent --add-port=110/tcp followed by sudo firewall-cmd --reload. Only open the port if your clients cannot be switched to port 995.
Any more questions?
Contact SupportWith a ZAP-Hosting VPS, you have root access, can set up services and firewall rules yourself, and can immediately see which ports are open.
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