Port
Port 25 — SMTP
Port 25 (TCP) is used by SMTP. Simple Mail Transfer Protocol — server-to-server email delivery.
Port 25 at a glance
| Property | Value |
|---|---|
| Port number | 25 |
| Transport | TCP |
| Service | SMTP |
| Category | Well-known port |
What it is used for
Simple Mail Transfer Protocol — server-to-server email delivery.
Security considerations
Often abused for spam relay. Use authenticated submission (587) and TLS.
See our full TCP/UDP port reference and learn how firewalls filter ports in the CyberOps course.
Frequently asked questions
What is port 25 used for?
Port 25 (TCP) is used by SMTP. Simple Mail Transfer Protocol — server-to-server email delivery.
Is port 25 TCP or UDP?
Port 25 uses TCP.
Is it safe to open port 25?
Often abused for spam relay. Use authenticated submission (587) and TLS.
Related
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