Should not be public
Port 110 — POP3
Legacy mail retrieval that downloads messages to one device.
Port
110
Service
POP3
Protocol
TCP
Security guidance
Unencrypted. Use POP3S (995) or, better, IMAP over TLS (993).
Is port 110 open on your server?
Test it from outside your network — the only view that matters.
Other common ports
20 · FTP data
21 · FTP control
22 · SSH / SFTP
23 · Telnet
25 · SMTP
53 · DNS
80 · HTTP
123 · NTP
143 · IMAP
161 · SNMP
389 · LDAP
443 · HTTPS
445 · SMB
465 · SMTPS
587 · SMTP submission
993 · IMAPS
995 · POP3S
1433 · Microsoft SQL Server
1521 · Oracle Database
2082 · cPanel
2083 · cPanel (TLS)
3000 · Node.js / dev server
3306 · MySQL / MariaDB
3389 · RDP
5432 · PostgreSQL
5900 · VNC
6379 · Redis
8080 · HTTP alternate
8443 · HTTPS alternate
9200 · Elasticsearch
27017 · MongoDB