Post Office Protocol version 2 — obsolete since POP3 took 110 in 1988.
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.
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.
$ sudo lsof -nP -iTCP:109 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.