SK0-004 · Question #752
A technician added a new mail relay server to the network. During testing, the server fails to forward mail. Which of the following firewall ports should the technician check?
The correct answer is A. 25. Port 25 is the standard SMTP port used for server-to-server mail relay, which is exactly the function a mail relay server performs.
Question
A technician added a new mail relay server to the network. During testing, the server fails to forward mail. Which of the following firewall ports should the technician check?
Options
- A25
- B80
- C110
- D443
How the community answered
(38 responses)- A95% (36)
- B3% (1)
- C3% (1)
Why each option
Port 25 is the standard SMTP port used for server-to-server mail relay, which is exactly the function a mail relay server performs.
Port 25 is the well-known TCP port for SMTP (Simple Mail Transfer Protocol), the protocol used by mail servers to relay and forward messages between hosts. A firewall blocking outbound port 25 will prevent the relay server from establishing SMTP sessions with destination mail servers, causing all forwarding attempts to fail.
Port 80 is used for HTTP web traffic and has no role in email relay or SMTP communication.
Port 110 is used for POP3, which is a client-side mail retrieval protocol, not a server-to-server mail forwarding protocol.
Port 443 is used for HTTPS encrypted web traffic and is unrelated to SMTP mail relay operations.
Concept tested: SMTP port 25 for mail relay forwarding
Source: https://learn.microsoft.com/en-us/exchange/mail-flow/connectors/connector-selection
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