# WHATPORT(109)

## NAME

port 109 — POP2 — Post Office Protocol version 2 — obsolete since POP3 took 110 in 1988.

Protocol: TCP  
IANA registry

## DESCRIPTION

POP2, defined in RFC 937, is the second-generation mailbox pickup protocol: a client connects, sends HELO with a username and plaintext password, and retrieves messages with a small command set. POP3 on port 110 replaced it and is not backward compatible, so POP2 has been dead in practice for decades. Some old mail servers still compiled a POP2 listener into inetd, which is the only realistic way you meet it. Like POP3 without TLS, it sends credentials in the clear.

## EXPOSURE

**Do not expose.** Obsolete protocol with plaintext authentication and no TLS story; if 109 is open, the fix is to turn it off, not to firewall it.

## CHECK

```sh
sudo lsof -nP -iTCP:109 -sTCP:LISTEN
```

## SEE ALSO

- spec — [RFC 937 — Post Office Protocol Version 2](https://www.rfc-editor.org/rfc/rfc937.html) (rfc-editor.org)
- iana — [IANA Service Name and Transport Protocol Port Number Registry](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml) (iana.org)

---

HTML: <https://whatport.net/109/> · JSON: <https://whatport.net/109.json> · full dataset: <https://whatport.net/ports.json>