Port 25 — SMTP
Quick reference for TCP/UDP port 25, used by SMTP. Includes what the service does, security guidance and related ports.
What is port 25?
Simple Mail Transfer Protocol for sending email.
What port does SMTP use?
SMTP listens on port 25 by default.
Security guidance
High risk — do not expose to the internet
Port 25 (SMTP) is high-risk because the service it carries is a frequent target for credential attacks, brute force or unpatched-vulnerability scanning. Keep it bound to localhost or your VPN, never forward it directly on a router, and require strong authentication.
Related ports
Frequently asked
What is port 25 used for?+
Port 25 is the standard TCP/UDP port for SMTP. Simple Mail Transfer Protocol for sending email.
What port does SMTP use?+
SMTP listens on port 25 by default.
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