587
submission
TCP · 0x024B
Port 587 — submission
Port 587 carries Mail submission over TCP. Being at or below 1023, only root may open it on Unix.
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 submission (submission)
- Kind
- Protocol
- TCP
- Range
- Well-known
- Root needed
- Yes
- Hexadecimal
- 0x024B
- Binary
- 0000001001001011
- Two bytes
- 2 · 75
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 587 used for?
Mail submission (submission) uses it, over TCP.
Q. Does opening port 587 need root?
Yes. It is at or below 1023, so on Unix only root may open it.
Q. Which range does port 587 fall in?
Well-known (0–1023). In hex it is 0x024B.
Q. Does port 587 have a twin?
Not a separate one. It either was encrypted from the start or negotiates TLS on the same number.