This LPIC-2 practice question tests your understanding of dns, web and mail services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 administrator wants to restrict which clients can relay mail through the server. Which three smtpd restriction lists are typically used for this purpose? (Choose three.)
smtpd_helo_restrictions
Checks the HELO/EHLO hostname.
smtpd_data_restrictions
Why wrong: Checks message data, not relaying.
smtpd_sender_restrictions
Why wrong: Used for sender verification, not relaying decisions.
smtpd_client_restrictions
Controls which clients can connect.
smtpd_recipient_restrictions
Primary list for relaying decisions.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
smtpd_helo_restrictions
A is correct because `smtpd_helo_restrictions` allows the administrator to enforce checks based on the HELO/EHLO hostname presented by the client during the SMTP greeting. By using restrictions like `reject_invalid_helo_hostname` or `reject_non_fqdn_helo_hostname`, the server can block clients that provide suspicious or non-compliant HELO names, which is a common tactic to prevent unauthorized relay attempts.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
smtpd_helo_restrictions
Why this is correct
Checks the HELO/EHLO hostname.
Related concept
Read the scenario before looking for a memorised answer.
smtpd_data_restrictions
Why it's wrong here
Checks message data, not relaying.
smtpd_sender_restrictions
Why it's wrong here
Used for sender verification, not relaying decisions.
smtpd_client_restrictions
Why this is correct
Controls which clients can connect.
Related concept
Read the scenario before looking for a memorised answer.
smtpd_recipient_restrictions
Why this is correct
Primary list for relaying decisions.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse `smtpd_sender_restrictions` with relay control, but it only filters based on the sender address, not on whether the client is authorized to relay mail.
Detailed technical explanation
Under the hood, Postfix evaluates these restriction lists in a specific order: `smtpd_client_restrictions`, `smtpd_helo_restrictions`, `smtpd_sender_restrictions`, and finally `smtpd_recipient_restrictions`. The `smtpd_recipient_restrictions` list is the most common place to enforce relay control using `permit_mynetworks` and `reject_unauth_destination`, which checks the recipient domain against the server's relay domains and transport maps. In real-world scenarios, combining `smtpd_client_restrictions` with `smtpd_helo_restrictions` can block open relays from dynamic IP ranges or misconfigured clients before they even reach the recipient check.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
DNS, Web and Mail Services — This question tests DNS, Web and Mail Services — Read the scenario before looking for a memorised answer..
The correct answer is: smtpd_helo_restrictions — A is correct because `smtpd_helo_restrictions` allows the administrator to enforce checks based on the HELO/EHLO hostname presented by the client during the SMTP greeting. By using restrictions like `reject_invalid_helo_hostname` or `reject_non_fqdn_helo_hostname`, the server can block clients that provide suspicious or non-compliant HELO names, which is a common tactic to prevent unauthorized relay attempts.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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.
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