25
smtp
TCP · 0x0019
Port 25 — smtp
Port 25 carries Mail sending over TCP. Being at or below 1023, only root may open it on Unix. Its encrypted twin is 465.
0–1023. On Unix only root may open one.
Where it sits in 65535
A port number is 16 bits, so it stops at 65535. The narrow band at the left is everything up to 1023.
065535
- Service
- Mail sending (smtp)
- Kind
- Protocol
- TCP
- Range
- Well-known
- Root needed
- Yes
- Hexadecimal
- 0x0019
- Binary
- 0000000000011001
- Two bytes
- 0 · 25
- Encrypted twin
- 465
Same kind
Sending mail out and fetching it back.
Ports next to it
How to read this
- A port number is 16 bits, so it runs 0 to 65535. There is no port 65536.
- Opening anything at or below 1023 needs root on Unix.
- Plain and encrypted often live on different numbers — 80 and 443, for one.
- Numbers like 3000 and 8080 were never registered; those are marked as custom.
Frequently asked questions
Q. What is port 25 used for?
Mail sending (smtp) uses it, over TCP.
Q. Does opening port 25 need root?
Yes. It is at or below 1023, so on Unix only root may open it.
Q. Which range does port 25 fall in?
Well-known (0–1023). In hex it is 0x0019.
Q. Is there an encrypted version of port 25?
Port 465 does the same thing wrapped in TLS.