Expose with care
Port 25 — SMTP
Server-to-server email delivery. Mail servers talk to each other on this port.
Port
25
Service
SMTP
Protocol
TCP
Security guidance
Needed on a mail server, pointless elsewhere. Many home and cloud providers block outbound 25 to limit spam.
Is port 25 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
53 · DNS
80 · HTTP
110 · POP3
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