Port 110 supports POP3 and pop3 (UDP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
Unencrypted or STARTTLS-capable POP3 mailbox retrieval.
Legacy mail clients downloading messages from a mailbox server.
Client to server
Prefer POP3S on 995 or another explicitly secured configuration; disable plaintext authentication.
pop3 (UDP reference coverage) is documented as a network service convention for port 110 over UDP.
Use this reference entry when identifying or validating systems documented to use 110/UDP.
Varies
Confirm the listening process and current vendor documentation before permitting traffic; a listed convention does not prove the active service or its security posture.