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Question

Difficulty: MediumNetwork Host Services and Server Roles

Employees at a corporate office report that while they can successfully receive emails from external partners, all attempts to send outgoing messages to external domains fail with a connection timeout. An IT technician checks the firewall logs and discovers that outbound traffic on TCP port 25 is being dropped at the network perimeter. Which of the following network host service roles is directly responsible for routing these outbound email transmissions?

  1. Mail serverAnswer
  2. B
    DNS server
  3. C
    DHCP server
  4. D
    Web server

Answer

Mail server
A mail server utilizes Simple Mail Transfer Protocol (SMTP) over TCP port 25 to send and relay outbound email messages across the internet. When TCP port 25 is blocked at the edge firewall, outbound email delivery fails while inbound retrieval protocols (such as IMAP or POP3) remain unaffected.

Step-by-Step Solution

1
Analyze the technical issue and blocked traffic details.
Outbound email transmission is failing because TCP port 25 traffic is blocked by the perimeter firewall.
Identifying TCP port 25 clarifies which host protocol and service role is affected.
2
Associate TCP port 25 with the matching network service protocol.
Simple Mail Transfer Protocol (SMTP) operates on TCP port 25.
SMTP is the standard protocol for sending and relaying mail between mail servers.
3
Identify the server role that runs SMTP service for outbound mail delivery.
The mail server is the network host role responsible for outbound email transmission.
Unblocking port 25 restores the mail server's capability to transfer mail to external domains.

Key Concept

Mail Server Roles and SMTP Protocol (Port 25)
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Topics

Network Host Services and Server Roles

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