This CEH practice question tests your understanding of enumeration and system hacking. 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 penetration tester is attempting to enumerate user accounts on a mail server. They connect to port 25 and issue the commands `VRFY root` and `EXPN support`. Which protocol is being targeted?
LDAP
Why wrong: LDAP uses port 389 and employs search operations, not VRFY/EXPN.
SMTP
Correct. VRFY and EXPN are SMTP commands used for user enumeration.
SMB
Why wrong: SMB uses port 445; it does not use SMTP commands.
SNMP
Why wrong: SNMP uses ports 161/162 and community strings, not VRFY/EXPN.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SMTP
The commands VRFY and EXPN are SMTP (Simple Mail Transfer Protocol) commands defined in RFC 821 and RFC 5321. VRFY is used to verify whether a mailbox exists on the server, while EXPN expands a mailing list alias to reveal its members. Since the tester connected to port 25 (the default SMTP port) and issued these commands, SMTP is the protocol being targeted.
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.
LDAP
Why it's wrong here
LDAP uses port 389 and employs search operations, not VRFY/EXPN.
SMTP
Why this is correct
Correct. VRFY and EXPN are SMTP commands used for user enumeration.
Related concept
Read the scenario before looking for a memorised answer.
SMB
Why it's wrong here
SMB uses port 445; it does not use SMTP commands.
SNMP
Why it's wrong here
SNMP uses ports 161/162 and community strings, not VRFY/EXPN.
Common exam traps
The trap here is that candidates may confuse SMTP commands with other protocol operations, such as associating VRFY with LDAP directory lookups or EXPN with SNMP expansion, because they focus on the word 'enumerate' rather than the specific port and command syntax.
Trap categories for this question
Command / output trap
SMB uses port 445; it does not use SMTP commands.
Detailed technical explanation
Under the hood, SMTP servers often disable VRFY and EXPN by default in modern configurations to prevent user enumeration, as these commands can be abused for reconnaissance. In a real-world scenario, a penetration tester might find these commands enabled on legacy or misconfigured mail servers, allowing them to harvest valid email addresses for phishing campaigns. The EXPN command can also reveal internal mailing list structures, which may expose sensitive group memberships.
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 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.
What to study next
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FAQ
Enumeration and System Hacking — This question tests Enumeration and System Hacking — Read the scenario before looking for a memorised answer..
The correct answer is: SMTP — The commands VRFY and EXPN are SMTP (Simple Mail Transfer Protocol) commands defined in RFC 821 and RFC 5321. VRFY is used to verify whether a mailbox exists on the server, while EXPN expands a mailing list alias to reveal its members. Since the tester connected to port 25 (the default SMTP port) and issued these commands, SMTP is the protocol being targeted.
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 24, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH exam.
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