Web

PortProtocolService
80TCPHTTP
443TCP, UDP (QUIC)HTTPS / HTTP/3
8080, 8000TCPHTTP — common alternates
8443TCPHTTPS — common alternate

Mail

PortProtocolService
25TCPSMTP (server-to-server)
465TCPSMTPS (implicit TLS)
587TCPSMTP submission (STARTTLS)
110TCPPOP3
995TCPPOP3 over TLS
143TCPIMAP
993TCPIMAP over TLS

Remote access & file transfer

PortProtocolService
22TCPSSH and SFTP
21TCPFTP (control)
20TCPFTP (data)
23TCPTelnet (deprecated — never use over the Internet)
3389TCPRDP — Windows Remote Desktop
5900TCPVNC

DNS & network services

PortProtocolService
53UDP, TCPDNS
853TCPDNS over TLS (DoT)
67, 68UDPDHCP server / client
123UDPNTP — network time
161UDPSNMP
514UDPSyslog

Databases & caches

PortService
3306MySQL / MariaDB
5432PostgreSQL
1433Microsoft SQL Server
1521Oracle
27017MongoDB
6379Redis
11211Memcached
9200Elasticsearch (HTTP)

Messaging & streaming

PortService
5672AMQP — RabbitMQ
9092Kafka
1883MQTT
8883MQTT over TLS
!

Never bind a database directly to a public interface. Even with strong authentication, a database port open to the Internet is a brute-force target and a vulnerability when the next CVE drops. Tunnel over SSH, bind to localhost behind a VPN, or use a managed service with private networking.