Dictionary · Protocols and Ports
SMTP
SMTP — Simple Mail Transfer Protocol
Email · Beginner
The protocol that transfers email between mail servers. Port 25 is the traditional server-to-server port. Authenticated submission commonly uses 587, and wrapped encryption may use 465.
This moves a message toward its destination server. Reading mail in a mailbox uses a different protocol. Submission from a person's mail app should require authentication.
Example: A company mail server accepts a message and relays it to the recipient's mail server on the traditional transfer port.
Ports
- TCP 25 — Server-to-server transfer
- TCP 587 — Authenticated submission
- TCP 465 — Implicit encrypted submission
Common misconception
- This protocol delivers mail between servers. It is not the usual protocol a person uses to open a mailbox and read old messages.