The answer is that the user principal name (UPN) suffix for users is not a verified domain in Microsoft Entra ID. This is the most likely cause of a UPN mismatch login failure because even when password hash synchronization completes successfully, Entra ID must recognize the domain portion of the UPN—such as @contoso.local—as a custom verified domain in the cloud. Without verification, the authentication request cannot be routed to the correct tenant, so users are blocked from signing in despite a green sync status. On the MS-102 exam, this scenario tests your understanding that sync success does not guarantee login success; the common trap is assuming a successful sync means all credentials are usable. The key distinction is that sync replicates objects, but login requires domain ownership. Memory tip: think “Sync is green, but domain unseen—UPN mismatch kills the login scene.”
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.
Your Microsoft 365 tenant has been configured with Microsoft Entra ID Connect synchronization from on-premises Active Directory. Users are unable to log in to Microsoft 365 services. You check the synchronization status and see that the last sync was successful. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The user principal name (UPN) suffix for users is not a verified domain in Microsoft Entra ID.
The most likely cause is that the UPN suffix for users is not a verified domain in Microsoft Entra ID. Even though password hash synchronization is enabled and the last sync was successful, if the UPN suffix (e.g., @contoso.local) does not match a custom domain verified in Entra ID, users cannot sign in because Entra ID cannot route authentication to the correct tenant. The sync process will complete without error, but login fails because the UPN is not recognized as a valid domain in the cloud.
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.
✗
The firewall is blocking authentication requests to Microsoft 365.
Why it's wrong here
Blocked firewalls would affect sync as well.
✗
The on-premises Active Directory is not reachable from the sync server.
Why it's wrong here
If unreachable, sync would fail.
✗
Password hash synchronization is disabled.
Why it's wrong here
If disabled, users would see an error about password mismatch, but sync would still succeed.
✓
The user principal name (UPN) suffix for users is not a verified domain in Microsoft Entra ID.
Why this is correct
UPN mismatch is a common cause of login failure after successful sync.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful sync means all authentication components are working, but Microsoft deliberately tests the distinction between object synchronization success and domain verification failure, which causes login to fail despite a green sync status.
Detailed technical explanation
How to think about this question
Under the hood, Microsoft Entra ID Connect synchronizes the on-premises UPN (userPrincipalName attribute) to the cloud UserPrincipalName. If the domain portion of that UPN is not verified in Entra ID, the cloud directory treats the user as having an unverified domain (like .onmicrosoft.com) and login fails because the authentication endpoint cannot map the domain to a tenant. This is a common misconfiguration when on-premises UPNs use internal DNS suffixes (e.g., contoso.local) that are not added as custom domains in Entra ID. The fix is to either add and verify the custom domain or change the UPN suffix to the verified domain using tools like IdFix.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: The user principal name (UPN) suffix for users is not a verified domain in Microsoft Entra ID. — The most likely cause is that the UPN suffix for users is not a verified domain in Microsoft Entra ID. Even though password hash synchronization is enabled and the last sync was successful, if the UPN suffix (e.g., @contoso.local) does not match a custom domain verified in Entra ID, users cannot sign in because Entra ID cannot route authentication to the correct tenant. The sync process will complete without error, but login fails because the UPN is not recognized as a valid domain in the cloud.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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