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Port 25: SMTP (Simple Mail Transfer Protocol)

SMTP Port 25 is used for server-to-server email routing and delivery across Mail Transfer Agents (MTAs).

Protocol
TCP
Category
Email Delivery
Common Services
Postfix, Exim, Sendmail, Microsoft Exchange

What is Port 25 and How Does It Work?

SMTP Port 25 is used for server-to-server email routing and delivery across Mail Transfer Agents (MTAs).

Security Vulnerabilities & Attack Vectors on Port 25

Open relay misconfigurations on port 25 allow spammers to send unauthorized emails. Many residential ISPs block outbound port 25.

Auditing & Scanning Port 25 with Nmap

Run the following command to check if Port 25 is reachable and determine service fingerprints:

nmap -p 25 --script smtp-open-relay,smtp-enum-users

Frequently Asked Questions

How do I check if Port 25 is open?
Use cyber-tool.org diagnostic tools or run 'nc -zv 25' in your terminal to verify open socket connections.
Is it safe to leave Port 25 open to the internet?
Exposing Port 25 (SMTP (Simple Mail Transfer Protocol)) publicly introduces potential exposure. Protect it with IP whitelisting, firewalls, and encryption.