MS-102 Deploy and manage a Microsoft 365 tenant Practice Question
You are a Microsoft 365 administrator. A user reports that they cannot send emails to a specific external domain. You check the Exchange Admin Center and see that the domain is not blocked. What should you check next?
⚠ Common exam trap
Candidates often assume domain blocking only occurs in the spam filter or outbound policies, overlooking that transport rules can enforce granular domain-based restrictions that are invisible in those sections.
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
✓
Check the mail flow rules (transport rules) in Exchange Online.
Mail flow rules (transport rules) in Exchange Online can block or redirect messages based on conditions like sender, recipient domain, or message content, even if the domain is not listed in any block list. Since the domain is not blocked in the spam filter or outbound policies, a transport rule is the most likely cause of the issue, as it can silently reject or quarantine messages without appearing in the standard block lists.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Verify that the user has a full mailbox and is not over the send limit.
Why it's wrong here
A full mailbox or exceeding the per-user send limit would trigger a non-delivery report (NDR) or block all outgoing mail, not selectively fail for one specific recipient domain. These limits are enforced at the mailbox or transport level based on the sender's quota and send rate, independent of the destination domain. Since the issue is domain-specific, this check would not diagnose the problem.
- ✗
Review the outbound spam filter policy.
Why it's wrong here
The outbound spam filter policy evaluates message content, volume, and sending patterns to detect compromised accounts or bulk spam, rather than blocking specific recipient domains. It applies actions (like quarantine or rejection) to outbound mail broadly, and would not cause a failure isolated to one particular domain. Unless the user's outbound pattern is spammy overall, this policy is not the logical first place to investigate.
- ✓
Check the mail flow rules (transport rules) in Exchange Online.
Why this is correct
Mail flow rules (transport rules) can contain conditions that match the recipient domain and actions such as reject, redirect, or silently drop the message. If a user can send to all domains except one, a transport rule targeting that domain is the most direct cause, especially after the blocked sender list is ruled out. Reviewing these rules in the Exchange admin center under Mail flow > Rules will reveal any applicable rule and its action.
- ✗
Check the spam filter policy to see if the domain is on the blocked sender list.
Why it's wrong here
You have already verified that the domain is not on the blocked sender list, so rechecking the spam filter policy is redundant and would not yield new information. Spam filter policies apply organization-wide domain blocks, which would affect all users, whereas the issue is user-specific. A domain-specific, user-specific failure points instead to a transport rule or an individual mailbox exception, not the spam filter policy.
Go deeper
Related to this question
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Microsoft 365 Tenant Setup
Key term
Transport rule
A Transport rule is a set of conditions and actions within Microsoft Exchange Online or Exchange Server that automatically processes email messages during transit based on defined criteria.
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.
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JA
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.