SK0-004 · Question #422
An administrator is setting up a new mail server on the network and wants to open necessary ports to allow POP3 protocol for mail delivery. Which of the following ports should be opened in the…
The correct answer is B. 110. POP3 (Post Office Protocol version 3) is assigned port 110 for standard unencrypted mail retrieval, and this port must be opened on firewalls to permit POP3 client-to-server communication.
Question
An administrator is setting up a new mail server on the network and wants to open necessary ports to allow POP3 protocol for mail delivery. Which of the following ports should be opened in the internal and external firewalls?
Options
- A101
- B110
- C123
- D161
How the community answered
(71 responses)- A1% (1)
- B93% (66)
- C4% (3)
- D1% (1)
Why each option
POP3 (Post Office Protocol version 3) is assigned port 110 for standard unencrypted mail retrieval, and this port must be opened on firewalls to permit POP3 client-to-server communication.
Port 101 is not assigned to POP3 or any standard email protocol by IANA and would not enable POP3 mail delivery.
Port 110 is the IANA-assigned well-known port for POP3, as originally defined in RFC 1939, and is used by mail clients to connect to a mail server and retrieve messages over an unencrypted channel. Both internal and external firewalls must allow TCP traffic on port 110 for POP3 to function across network segments. If encrypted POP3 over SSL/TLS is required, port 995 would be used instead.
Port 123 is the well-known port for NTP (Network Time Protocol), used for clock synchronization between hosts, not for email retrieval.
Port 161 is the well-known port for SNMP (Simple Network Management Protocol), used for polling and managing network devices, not for mail delivery.
Concept tested: POP3 standard port number and firewall configuration
Source: https://datatracker.ietf.org/doc/html/rfc1939
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