LPIC-2 DNS, Web and Mail Services Practice Question
This LPIC-2 practice question tests your understanding of dns, web and mail services. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
An organization's Postfix mail server is being used as an open relay. The administrator wants to restrict relaying to only authenticated users from the internal network. Which combination of settings is correct?
Option D is correct because it enforces relaying restrictions in the correct order: first permit mail from trusted internal networks (permit_mynetworks), then permit authenticated users (permit_sasl_authenticated), and finally reject all other unauthorized destinations (reject_unauth_destination). This ensures that only authenticated users or hosts in mynetworks can relay, while blocking open relay attempts from external unauthenticated sources.
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.
Allows internal networks and authenticated users before rejecting unauthorized destinations.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often place reject_unauth_destination first to block open relays, forgetting that it must come after permit_mynetworks and permit_sasl_authenticated to avoid blocking legitimate internal or authenticated relays.
Detailed technical explanation
How to think about this question
Postfix evaluates smtpd_recipient_restrictions in order until a permit or reject action is found; placing reject_unauth_destination early would deny all unauthenticated relays, including those from mynetworks, unless mynetworks is checked first. The permit_sasl_authenticated check relies on SASL authentication having already occurred (typically via smtpd_sasl_auth_enable), and it must appear after permit_mynetworks to allow internal hosts without authentication. In real-world scenarios, misordering these restrictions is a common cause of either open relays or broken internal mail flow.
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: smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination — Option D is correct because it enforces relaying restrictions in the correct order: first permit mail from trusted internal networks (permit_mynetworks), then permit authenticated users (permit_sasl_authenticated), and finally reject all other unauthorized destinations (reject_unauth_destination). This ensures that only authenticated users or hosts in mynetworks can relay, while blocking open relay attempts from external unauthenticated sources.
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.
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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