The answer is the MX record, which must be added to the public DNS zone to route email to Exchange Online. This record type, short for Mail Exchange, tells sending mail servers where to deliver messages for your custom domain, such as contoso.com. Without it, inbound emails cannot reach the Exchange Online mail exchanger, typically formatted as contoso-com.mail.protection.outlook.com with a priority of 0. On the MS-102 exam, this question tests your understanding of DNS configuration for hybrid or cloud-only mail flow, often appearing as a scenario where users cannot receive email after domain verification. A common trap is confusing the MX record with CNAME or TXT records; remember that only the MX record controls mail routing, not domain ownership verification. For a memory tip, think “MX = Mail eXchange” and that it must point to the .mail.protection.outlook.com endpoint—if emails aren’t arriving, check that the MX record is present and correctly prioritized.
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. 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.
An administrator has added a custom domain 'contoso.com' to their Microsoft 365 tenant and verified ownership. However, users are unable to receive emails sent to their custom domain. Which type of DNS record must the administrator add in the public DNS zone to route emails to Exchange Online?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
MX record
The MX (Mail Exchange) record is the DNS record type that directs email messages to a specific mail server. For Exchange Online, the MX record must point to the tenant's mail exchanger (e.g., contoso-com.mail.protection.outlook.com) with a priority value (typically 0). Without this record, sending mail servers cannot route inbound emails to the custom domain's mailbox store in 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.
✗
TXT record
Why it's wrong here
TXT records are used for domain verification and SPF, DKIM, DMARC. They do not route email.
✓
MX record
Why this is correct
An MX record specifies the mail exchange server for the domain. For Exchange Online, it must point to the Microsoft mail exchanger.
Related concept
Read the scenario before looking for a memorised answer.
✗
CNAME record
Why it's wrong here
A CNAME record is typically used for autodiscover (e.g., autodiscover.contoso.com) or other aliases, not for mail routing.
✗
SPF record
Why it's wrong here
SPF (TXT) record authorizes sending servers, but does not route incoming mail.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the purpose of MX records with SPF or TXT records, thinking that SPF alone enables email delivery, when in fact MX records are the fundamental requirement for inbound mail routing.
Detailed technical explanation
How to think about this question
When a sending SMTP server looks up the MX record for contoso.com, it receives the hostname of the Exchange Online gateway (e.g., contoso-com.mail.protection.outlook.com) and a priority value. Lower priority numbers are preferred; if multiple MX records exist, the sender tries the lowest priority first. This process is defined in RFC 5321 and RFC 974, and without the MX record, the sender will fail to deliver the message, resulting in a non-delivery report (NDR).
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this MS-102 question in full detail.
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: MX record — The MX (Mail Exchange) record is the DNS record type that directs email messages to a specific mail server. For Exchange Online, the MX record must point to the tenant's mail exchanger (e.g., contoso-com.mail.protection.outlook.com) with a priority value (typically 0). Without this record, sending mail servers cannot route inbound emails to the custom domain's mailbox store in 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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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator has added the custom domain 'contoso.co.uk' to their Microsoft 365 tenant and verified ownership. Users now need to receive email at @contoso.co.uk. Which DNS record must the administrator add in the public DNS zone to route emails to Exchange Online?
medium
✓ A.Add an MX record pointing to <tenant>.mail.protection.outlook.com
B.Add a CNAME record for autodiscover
C.Add an SPF record
D.Add a DKIM record
Why A: To route email for a custom domain to Exchange Online, you must add an MX record in the public DNS zone that points to the Exchange Online mail exchanger. The correct target is <tenant>.mail.protection.outlook.com, where <tenant> is your initial tenant name (e.g., contoso-com). This MX record tells sending mail servers to deliver messages for @contoso.co.uk to Microsoft's email infrastructure.
Variation 2. A company recently added the custom domain 'contoso.com' to their Microsoft 365 tenant. Users report that they cannot receive external email sent to their new domain addresses. The administrator confirmed that the domain status shows 'Active' in the Microsoft 365 admin center. What is the most likely cause of this issue?
easy
A.The domain was not verified with a TXT record.
✓ B.The MX record for the domain is missing or points to an incorrect mail server.
C.The SPF record for the domain is missing or incorrectly configured.
D.The custom domain was not added to the user's primary email address.
Why B: The domain status 'Active' in the Microsoft 365 admin center indicates that the domain has been successfully verified and added to the tenant. However, for external email to be delivered to users at that domain, the public MX record in DNS must point to Microsoft 365's mail servers (e.g., contoso-com.mail.protection.outlook.com). If the MX record is missing or points to an incorrect server, external senders cannot route email to the tenant, even though the domain is verified and active.
Last reviewed: Jun 11, 2026
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