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 mail server running Postfix is deferring messages for a local user. The mail log shows 'status=deferred (mailbox is locked)'. 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 user's mailbox is currently being accessed by a POP3 client.
The 'mailbox is locked' message in Postfix logs indicates that the mailbox file is currently locked by another process, typically a POP3 or IMAP client that has the mailbox open for exclusive access. Postfix defers delivery because it cannot acquire the necessary lock to write to the mailbox, ensuring data integrity. This is a standard behavior defined by the mailbox locking mechanism (e.g., fcntl, dotlock) used by the MTA and MDA.
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 user's mailbox is currently being accessed by a POP3 client.
Why this is correct
Concurrent access by a mail client can lock the mailbox file, causing Postfix to defer delivery with 'mailbox is locked'.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The filesystem containing the mail spool is out of inodes.
Why it's wrong here
Out of inodes would cause a 'No space left on device' error, not a mailbox lock.
✗
The disk quota for the user has been exceeded.
Why it's wrong here
Quota exceeded errors are reported as 'mailbox is full' or 'quota exceeded', not 'mailbox is locked'.
✗
The Postfix process lacks write permission to the mailbox.
Why it's wrong here
Permission issues typically result in 'permission denied' errors, not 'mailbox is locked'.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'mailbox is locked' with permission or quota issues, but the lock message specifically points to a concurrent access conflict, not a filesystem or authorization problem.
Detailed technical explanation
How to think about this question
Postfix uses mailbox locking via fcntl() or dotlock files to prevent concurrent writes from multiple processes (e.g., another MTA delivery or a POP3 client). The lock is typically held by the POP3/IMAP daemon while the user retrieves messages, causing Postfix to defer delivery until the lock is released. In real-world scenarios, this often occurs when a user leaves a POP3 client open in 'keep mail on server' mode, or when an IMAP client holds a long-lived lock on the INBOX.
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 practitioner preparing for the LPIC-2 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 user's mailbox is currently being accessed by a POP3 client. — The 'mailbox is locked' message in Postfix logs indicates that the mailbox file is currently locked by another process, typically a POP3 or IMAP client that has the mailbox open for exclusive access. Postfix defers delivery because it cannot acquire the necessary lock to write to the mailbox, ensuring data integrity. This is a standard behavior defined by the mailbox locking mechanism (e.g., fcntl, dotlock) used by the MTA and MDA.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This LPIC-2 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-2 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.