- A
No additional step; subdomains are automatically verified after the root domain is verified.
Why wrong: Subdomains are not automatically verified. They must be added and verified separately.
- B
Add 'sales.contoso.com' as a custom domain and verify ownership by adding a DNS TXT record.
To use a subdomain, it must be added as a custom domain in the Microsoft 365 admin center and verified via a DNS TXT record or other allowed methods.
- C
Create a subdomain in Exchange Online using the Exchange admin center.
Why wrong: Exchange Online does not create subdomains; the subdomain must first be registered and verified as a custom domain in Microsoft 365.
- D
Modify the SPF record for the root domain to include 'sales.contoso.com'.
Why wrong: SPF records are used for email authentication, not for domain verification. The subdomain must still be verified separately.
Quick Answer
The correct answer is to add 'sales.contoso.com' as a custom domain and verify ownership by adding a DNS TXT record. This is required because in Microsoft 365, domain verification is per-domain, not hierarchical; verifying the root domain contoso.com does not automatically extend trust to any subdomain. Each subdomain is treated as a separate namespace that must be explicitly added in the Microsoft 365 admin center and validated with a unique TXT record provided by the system. On the MS-102 exam, this concept tests your understanding of domain management and DNS configuration, often appearing as a trap where candidates assume subdomain verification is inherited. A common memory tip is to think of it like a building’s security: a keycard for the main entrance (root domain) does not unlock every individual office (subdomain) inside. Remember the mnemonic “Subdomain = Separate Domain” to avoid missing this step when you verify subdomain for email exchange online.
MS-102 Deploy and manage a Microsoft 365 tenant Practice Question
This MS-102 practice question tests your understanding of deploy and manage a microsoft 365 tenant. 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.
A company has registered the custom domain 'contoso.com' and wants to host email for the subdomain 'sales.contoso.com' in Exchange Online. They have already verified the root domain. What additional step is required?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add 'sales.contoso.com' as a custom domain and verify ownership by adding a DNS TXT record.
In Microsoft 365, verifying a root domain (e.g., contoso.com) does not automatically verify its subdomains. Each subdomain must be added as a separate custom domain in the Microsoft 365 admin center and verified by adding a unique DNS TXT record provided by Microsoft. This ensures that the organization proves ownership of the subdomain before it can be used for services like Exchange Online.
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.
- ✗
No additional step; subdomains are automatically verified after the root domain is verified.
Why it's wrong here
Subdomains are not automatically verified. They must be added and verified separately.
- ✓
Add 'sales.contoso.com' as a custom domain and verify ownership by adding a DNS TXT record.
Why this is correct
To use a subdomain, it must be added as a custom domain in the Microsoft 365 admin center and verified via a DNS TXT record or other allowed methods.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a subdomain in Exchange Online using the Exchange admin center.
Why it's wrong here
Exchange Online does not create subdomains; the subdomain must first be registered and verified as a custom domain in Microsoft 365.
- ✗
Modify the SPF record for the root domain to include 'sales.contoso.com'.
Why it's wrong here
SPF records are used for email authentication, not for domain verification. The subdomain must still be verified separately.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume domain verification in Microsoft 365 is hierarchical (like DNS delegation), but in reality, each subdomain is treated as an independent domain that must be explicitly added and verified.
Detailed technical explanation
How to think about this question
Under the hood, Microsoft 365 uses the Domain Ownership Verification protocol (RFC 8555-style) where a unique TXT record value is generated per domain. The verification process checks that the TXT record exists at the subdomain's DNS zone (e.g., sales.contoso.com) and matches the expected value. A real-world scenario: if you skip this step, users at sales.contoso.com cannot receive email in Exchange Online, and any attempt to add the subdomain as an accepted domain will fail until verification completes.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this MS-102 question test?
Deploy and manage a Microsoft 365 tenant — This question tests Deploy and manage a Microsoft 365 tenant — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add 'sales.contoso.com' as a custom domain and verify ownership by adding a DNS TXT record. — In Microsoft 365, verifying a root domain (e.g., contoso.com) does not automatically verify its subdomains. Each subdomain must be added as a separate custom domain in the Microsoft 365 admin center and verified by adding a unique DNS TXT record provided by Microsoft. This ensures that the organization proves ownership of the subdomain before it can be used for services like Exchange Online.
What should I do if I get this MS-102 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.
About these practice questions
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Last reviewed: Jun 11, 2026
This MS-102 practice question is part of Courseiva's free Microsoft 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 MS-102 exam.
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