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.
An attacker attempts to enumerate valid email users by connecting to an SMTP server and issuing the following commands: EHLO example.com, VRFY root, VRFY admin, VRFY user1. Which SMTP enumeration technique is being used?
RCPT TO
Why wrong: RCPT TO identifies recipients in the mail delivery process, but VRFY is used here.
MAIL FROM
Why wrong: MAIL FROM starts a mail transaction, not user enumeration.
EXPN
Why wrong: EXPN expands mailing lists, not individual users.
VRFY
VRFY asks the server to verify a mailbox name.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VRFY
Option D is correct because the VRFY command is specifically designed to verify whether a mailbox exists on an SMTP server. By issuing VRFY followed by usernames (root, admin, user1), the attacker can enumerate valid email users based on the server's responses (e.g., 250 or 251 for valid, 550 for invalid). This is a classic SMTP user enumeration technique.
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.
RCPT TO
Why it's wrong here
RCPT TO identifies recipients in the mail delivery process, but VRFY is used here.
MAIL FROM
Why it's wrong here
MAIL FROM starts a mail transaction, not user enumeration.
EXPN
Why it's wrong here
EXPN expands mailing lists, not individual users.
VRFY
Why this is correct
VRFY asks the server to verify a mailbox name.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse VRFY with EXPN, thinking both verify users, but EXPN expands aliases/groups while VRFY checks individual mailboxes.
Detailed technical explanation
The VRFY command, defined in RFC 821 and updated in RFC 5321, asks the SMTP server to confirm whether a mailbox is deliverable. Some servers may return a 250 response for valid users and 550 for invalid, but modern servers often disable VRFY or return ambiguous responses to prevent enumeration. In real-world attacks, if VRFY is blocked, attackers fall back to RCPT TO enumeration, which is slower but often still effective.
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: VRFY — Option D is correct because the VRFY command is specifically designed to verify whether a mailbox exists on an SMTP server. By issuing VRFY followed by usernames (root, admin, user1), the attacker can enumerate valid email users based on the server's responses (e.g., 250 or 251 for valid, 550 for invalid). This is a classic SMTP user enumeration technique.
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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