N10-009 Question 47
Single answer1.4 Explain common networking ports, protocols, services, and traffic types.A network administrator is migrating a branch office from an on-premises email server to a cloud-based messaging platform. After the migration, users can send email externally, but remote users report that they cannot securely retrieve messages on their mobile devices. A firewall review shows that outbound traffic is currently allowed only on TCP 25, 80, and 443. The mobile email application is configured to use a protocol that downloads mail to the client over an encrypted connection without requiring a web browser. Which additional outbound port should the administrator allow to support this requirement?
- A
TCP 110
- B
TCP 143
- C
TCP 465
- D
TCP 993
- E
TCP 995
Show answer and explanation
Correct answer: E
Explanation
The key to this question is matching the service behavior and the port. The scenario specifies secure retrieval of email, mobile client access, and a protocol that downloads messages to the client rather than synchronizing mailbox state. That points to POP3, and the secure version uses TCP 995. By contrast, POP3 on TCP 110 is not encrypted by default. IMAP on TCP 143 and IMAPS on TCP 993 are for mailbox synchronization and server-side message management rather than classic download-oriented retrieval. SMTP-related ports such as TCP 25 and TCP 465 are for message submission or relay, not retrieval. Network+ objectives commonly expect candidates to know both the function of protocols and their well-known ports, especially for services such as SMTP, POP3, and IMAP. These port assignments are consistent with standard operational references and common vendor documentation for email client configuration.
- A. Incorrect.
TCP 110 is used by POP3 in clear text by default. While POP3 does download messages to the client, this port does not provide the encrypted connection described in the scenario. A candidate might choose this option if they recognize POP3 but overlook the security requirement.
- B. Incorrect.
TCP 143 is used by IMAP. IMAP is commonly used for message synchronization rather than simple download-and-store behavior, and port 143 is not encrypted by default. This is a plausible distractor because IMAP is widely used by mobile clients, but it does not match the specific requirement for encrypted POP retrieval.
- C. Incorrect.
TCP 465 is commonly associated with SMTPS or authenticated SMTP submission over implicit TLS in many environments. SMTP is used for sending mail, not retrieving it. Someone might select this option because the scenario involves email and encryption, but the issue is with secure message retrieval.
- D. Incorrect.
TCP 993 is used for IMAPS, which provides encrypted IMAP access. Although it is secure and often used on mobile devices, IMAP is a synchronization protocol rather than the download-oriented protocol described in the scenario. This option is attractive if the reader focuses on mobile email and encryption but ignores the protocol behavior stated in the question.
- E. Correct.
TCP 995 is the correct answer. It is used for POP3 over SSL/TLS, often referred to as secure POP3. POP3 is the protocol that typically downloads messages to the client, and port 995 satisfies the requirement for an encrypted connection.