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Difficulty: MediumCommon Ports and Protocols

A system administrator is updating firewall access control lists to enable user workstations to securely send outbound messages and retrieve incoming messages from an enterprise mail server over TLS-encrypted sessions. Which TWO of the following port and protocol combinations must be permitted through the firewall to support these secure email services? (Select TWO.)

  1. TCP port 993 for IMAPSAnswer
  2. TCP port 587 for SMTP SubmissionAnswer
  3. C
    UDP port 993 for IMAPS
  4. D
    TCP port 110 for POP3S

Answer

The firewall must permit TCP port 993 for IMAPS and TCP port 587 for SMTP Submission.
Encrypted email retrieval using IMAP over SSL/TLS (IMAPS) standardly uses TCP port 993. Encrypted client email submission using SMTP with TLS standardly uses TCP port 587. Both ports must be open on the firewall to allow secure sending and receiving from mail clients.

Step-by-Step Solution

1
Identify the protocol requirements for encrypted email retrieval.
IMAP over TLS/SSL (IMAPS) provides secure mail retrieval on standard TCP port 993.
Unencrypted IMAP uses port 143, whereas encrypted IMAPS defaults to TCP port 993.
2
Identify the protocol requirements for encrypted outbound email submission.
SMTP Client Submission over TLS operates on TCP port 587.
Legacy unencrypted SMTP uses port 25, while secure client mail submission to an email broker uses TCP port 587.
3
Evaluate transport layer protocols and port mappings for the incorrect choices.
Rule out UDP-based transport for IMAP and incorrect port assignments for POP3S.
Email retrieval protocols require connection-oriented reliability (TCP), eliminating UDP choices, and POP3S operates on TCP 995 rather than TCP 110.

Key Concept

Standard Secure Mail Ports (IMAPS TCP 993, SMTP Submission TCP 587, POP3S TCP 995)
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Topics

Common Ports and Protocols

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