220-1101 Question 57
Single answerPorts and protocolsA technician is configuring a small office firewall after users report they can send email from their mail client but cannot download new messages from the company mail server when working remotely. The email application is configured to use a secure IMAP connection. Which port should the technician verify is allowed through the firewall?
- A
TCP 25
- B
TCP 110
- C
TCP 143
- D
TCP 993
Show answer and explanation
Correct answer: D
Explanation
This question tests practical knowledge of common email ports and the ability to apply that knowledge in a troubleshooting scenario. In real environments, sending and receiving email often rely on different protocols and ports, so partial functionality is a strong clue. SMTP commonly uses TCP 25 for server-to-server communication and often TCP 587 for client submission, while IMAP uses TCP 143 and secure IMAP typically uses TCP 993. POP3 uses TCP 110 and secure POP3 uses TCP 995. CompTIA A+ Core 1 expects candidates to recognize these standard ports and match them to the correct services during troubleshooting. This aligns with common vendor and standards documentation for internet mail services, including IANA service name and port number assignments and standard email client/server configuration best practices.
- A. Incorrect.
TCP 25 is used for SMTP, which is primarily responsible for sending email between mail servers and from clients to a mail server in many configurations. Because the users can already send email, this port is not the one associated with securely retrieving messages via IMAP.
- B. Incorrect.
TCP 110 is used for POP3, a protocol for downloading email from a server. However, the scenario specifically states the client is configured for a secure IMAP connection, not POP3. A common mistake is to confuse all incoming mail protocols as interchangeable.
- C. Incorrect.
TCP 143 is the standard port for IMAP without implicit TLS. Some environments can start with IMAP on 143 and then upgrade security with STARTTLS, but the question specifies a secure IMAP connection, which on A+ exams is typically associated with IMAPS on TCP 993.
- D. Correct.
TCP 993 is the correct answer because it is the standard port for IMAP over SSL/TLS, commonly referred to as secure IMAP or IMAPS. If this port is blocked on the firewall, users may be able to send mail successfully through SMTP while failing to retrieve messages securely through IMAP.