knownports / Ports 0–99 / Port 25
Port25
smtpSimple Mail Transfer
IANA has registered port 25 to smtp on TCP and UDP.
Registry entries
| Service | Protocols | Registered | Modified | RFCs | Other specs |
|---|---|---|---|---|---|
smtp | TCPUDP | — | Jun 5, 2017 | — | RFC-ietf-emailcore-rfc5321bis-43 |
Where it sits in the registry
Port 25 is one of 70 numbers with an assignment in ports 0–99 (70.0% of the range). 64 other numbers in the range are assigned on exactly the same transports, TCP and UDP, the usual pattern for older entries. The registry records no registration date for it, as for 69 other numbers in the range; dates were recorded mainly from 2002 on. IANA last modified the entry on June 5, 2017. No other number in the registry shares that modification date.
Status on each protocol
| Protocol | On port 25 | Other numbers with the same status | Nearest with the same status |
|---|---|---|---|
| TCP | assigned to smtp | 5,887 | 23 telnet |
| UDP | assigned to smtp | 5,500 | 23 telnet |
| SCTP | no entry | 5,999 | 23 telnet |
| DCCP | no entry | 6,080 | 23 telnet |
5,273 other assigned numbers in the registry have exactly this combination across all four protocols.
The nearest assigned numbers
| Port | Service | Label | Protocols | Registered | Distance |
|---|---|---|---|---|---|
| 21 | ftp | File Transfer Protocol [Control] | TCPUDPSCTP | — | 4 |
| 22 | ssh | The Secure Shell (SSH) Protocol | TCPUDPSCTP | — | 3 |
| 23 | telnet | — | TCPUDP | — | 2 |
| 27 | nsw-fe | NSW User System FE | TCPUDP | — | 2 |
| 29 | msg-icp | MSG ICP | TCPUDP | — | 4 |
| 31 | msg-auth | MSG Authentication | TCPUDP | — | 6 |
Other entries that mention smtp
The text smtp appears in the name or label of two other registry entries, every one shown here. It is a text match, not a statement that the services are related.
- 2390
rsmtp - no number,
pgpkey-mailto“PGP Key submission using SMTP”