MS-102 Deploy and manage a Microsoft 365 tenant Practice Question
A company adds and verifies the custom domain 'contoso.com' in their Microsoft 365 tenant. However, emails sent to new users at user@contoso.com bounce back. The existing MX record for contoso.com points to the on-premises mail server. What is the most likely cause of the bounce?
⚠ Common exam trap
A common mix-up: candidates confuse domain verification (a one-time DNS check) with ongoing mail routing (MX record), leading them to think verification failure is the cause, when in fact the MX record is the direct culprit.
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
✓
The MX record must be updated to point to Exchange Online
B is correct because the MX record for contoso.com still points to the on-premises mail server. When a user is created in Exchange Online with the domain contoso.com, inbound email is routed according to the MX record. Since the MX record directs mail to the on-premises server, which does not have a mailbox for the new user, the message bounces. To deliver mail to Exchange Online, the MX record must be updated to point to Exchange Online (e.g., contoso-com.mail.protection.outlook.com).
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 domain verification failed and needs to be repeated
Why it's wrong here
Domain verification is a one-time ownership check that proves you control the domain. Once Microsoft 365 confirms a TXT record (or other method) matches, the domain is marked verified and that status does not expire or require repetition. If the domain already shows as verified and email bounces, the cause is an external DNS routing problem, not a verification issue; re-running verification will not change where the old MX record sends mail.
- ✓
The MX record must be updated to point to Exchange Online
Why this is correct
The MX record is the DNS instruction that tells sending mail servers where to deliver messages for your domain. When you add a verified custom domain to Microsoft 365, you must change this record from your previous email provider to the Exchange Online endpoint (for example, contoso-com.mail.protection.outlook.com). If you leave the old MX value in place, inbound mail continues to route to the legacy mail server, which has no mailbox for the recipient, causing the bounce. Correcting the MX record is the precise fix for bounced incoming mail after domain provisioning.
- ✗
Users must be added to the domain in the admin center
Why it's wrong here
Users and their assigned domains are managed separately from DNS routing. If the users have Exchange Online licenses and their primary SMTP address already matches the verified contoso.com domain, they are fully provisioned in the cloud; re-adding them in the admin center will not change where external senders route messages. The bounce occurs because the MX record still points to the previous provider, meaning the mail never reaches Exchange Online where those mailboxes actually exist, so no user-side administrative action can overcome a DNS-level routing error.
- ✗
The SPF record is missing or misconfigured
Why it's wrong here
SPF (Sender Policy Framework) is a DNS record that authorizes which IPs may send email on behalf of your domain; it is designed to prevent spoofing and outbound mail rejection. It has no influence on the direction of inbound email because incoming routing is controlled exclusively by the MX record. If SPF were missing or misconfigured, external servers might flag or reject messages sent from your domain, but the symptom described—incoming mail bouncing for all users—would still be caused by the MX record pointing at the wrong destination, not by SPF.
Go deeper
Related to this question
Learn chapter
Microsoft 365 Tenant Setup
Key term
Exchange Online
Exchange Online is Microsoft's cloud-based email, calendar, and contact hosting service that is part of the Microsoft 365 suite, allowing organizations to manage corporate messaging without maintaining their own mail servers.
Key term
Microsoft 365
Microsoft 365 is a subscription-based cloud service from Microsoft that combines productivity tools like Office apps with security, device management, and online storage.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.