Port 109 is used for the Post Office Protocol version 2 (POP2), which is a protocol used to retrieve email messages from a mail server. However, this protocol is rarely used nowadays as most email servers and applications use the newer version, POP3.
Ports those registered with IANA are shown as official ports. The same port number may be unofficialy used by various services or applications. The official usage are listed separately below its usage may change from time to time.
Official
| Port | Protocol (TCP/UDP) | Title | Description | Port Type |
| Port 109 | tcp | pop2 | Post Office Protocol Version | WELL KNOWN PORT |
| Port 109 | udp | pop2 | Post Office Protocol Version | WELL KNOWN PORT |
UnOfficial
Unofficialy or sometimes with conflict, the same port may be used by different applications.
| Port | Protocol (TCP/UDP) | Description |