The correct interpretation is that the root user exists but is disabled, the admin mailing list exists, and unknown@domain.com does not exist, based on the SMTP enumeration response codes 252, 250, and 550. When you issue VRFY and receive a 252 code, it means the server acknowledges the user exists but cannot verify delivery—often because the account is disabled or the response is deliberately ambiguous to prevent full enumeration. EXPN returning 250 confirms the mailing list or alias is valid and expandable, while RCPT TO returning 550 indicates the mailbox does not exist on the server. On the Certified Ethical Hacker CEH exam, this scenario tests your ability to interpret SMTP response codes during reconnaissance, a common phase in footprinting and enumeration. A frequent trap is confusing 252 with 250—remember that 252 means “maybe” or disabled, not a fully active user. Memory tip: “252 is a maybe, 250 is a go, 550 is a no.”
CEH Enumeration and System Hacking Practice Question
This CEH practice question tests your understanding of enumeration and system hacking. 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.
During an SMTP enumeration, a penetration tester connects to the mail server on port 25 and issues the commands 'VRFY root', 'EXPN admin', and 'RCPT TO:unknown@domain.com'. The server responds with '252' for VRFY, '250' for EXPN, and '550' for RCPT TO. What does this indicate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The root user exists but is disabled, the admin mailing list exists, and unknown@domain.com does not exist
VRFY returns 252 if the user exists but is disabled (or ambiguous), EXPN returns 250 if the mailing list/alias exists, RCPT TO returns 550 if the mailbox does not exist. This allows enumerating valid users on the server.
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 root user exists but is disabled, the admin mailing list exists, and unknown@domain.com does not exist
Why this is correct
VRFY 252 indicates existence but disabled, EXPN 250 indicates existence, RCPT TO 550 indicates non-existence.
Related concept
Read the scenario before looking for a memorised answer.
✗
The server has open relay enabled
Why it's wrong here
Open relay would accept email to any domain, not indicated by these responses.
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
The commands were accepted, so SMTP is running.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 CEH 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Enumeration and System Hacking — This question tests Enumeration and System Hacking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The root user exists but is disabled, the admin mailing list exists, and unknown@domain.com does not exist — VRFY returns 252 if the user exists but is disabled (or ambiguous), EXPN returns 250 if the mailing list/alias exists, RCPT TO returns 550 if the mailbox does not exist. This allows enumerating valid users on the server.
What should I do if I get this CEH question wrong?
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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