LPIC-2 DNS, Web and Mail Services Practice Question
This LPIC-2 practice question tests your understanding of dns, web and mail services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Postfix mail server is configured to use Dovecot SASL for authentication. Users report that they can send emails but are prompted for password repeatedly and see "SASL authentication failed" in the logs. The Dovecot SASL socket is configured correctly. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The postfix user does not have permission to access the Dovecot auth socket.
The correct answer is B because the most common cause of repeated password prompts and 'SASL authentication failed' errors when Postfix is configured to use Dovecot SASL is a permissions issue on the Dovecot auth socket. Even if the socket path is correct in Postfix's `smtpd_sasl_path`, the Postfix process (typically running as the `postfix` user) must have read/write access to that socket file. Without proper permissions, Postfix cannot communicate with Dovecot's authentication service, causing SASL failures despite correct authentication mechanisms and enabled settings.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The mynetworks parameter in Postfix is set to the wrong subnet.
Why it's wrong here
mynetworks controls relaying, not SASL authentication.
✓
The postfix user does not have permission to access the Dovecot auth socket.
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Dovecot auth mechanism is set to 'login' but Postfix expects 'PLAIN'.
Why it's wrong here
Postfix can negotiate mechanisms; a mismatch would cause a different error.
✗
The smtpd_sasl_auth_enable parameter is set to no.
Why it's wrong here
If disabled, no authentication would be offered.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on authentication mechanism mismatches or network-level settings, overlooking the fundamental Unix permission issue on the SASL socket, which is a classic gotcha in Postfix-Dovecot integration.
Detailed technical explanation
How to think about this question
Under the hood, Dovecot SASL uses a Unix domain socket (e.g., `/var/spool/postfix/private/auth`) to communicate with Postfix. The Postfix `smtpd` process runs as the `postfix` user, while Dovecot's auth socket is often owned by `dovecot:dovecot` with restrictive permissions (e.g., 0600). A common real-world scenario is that the socket is placed inside Postfix's chroot jail (if enabled), requiring careful permission and ownership adjustments—often solved by adding the `postfix` user to the `dovecot` group or changing the socket's group permissions to 0660.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
DNS, Web and Mail Services — This question tests DNS, Web and Mail Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The postfix user does not have permission to access the Dovecot auth socket. — The correct answer is B because the most common cause of repeated password prompts and 'SASL authentication failed' errors when Postfix is configured to use Dovecot SASL is a permissions issue on the Dovecot auth socket. Even if the socket path is correct in Postfix's `smtpd_sasl_path`, the Postfix process (typically running as the `postfix` user) must have read/write access to that socket file. Without proper permissions, Postfix cannot communicate with Dovecot's authentication service, causing SASL failures despite correct authentication mechanisms and enabled settings.
What should I do if I get this LPIC-2 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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