This MS-900 practice question tests your understanding of describe microsoft 365 apps and services. 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.
Exhibit
Refer to the exhibit.
```kql
EmailEvents
| where Timestamp > ago(7d)
| where EmailDirection == "Inbound"
| where DeliveryAction == "Blocked"
| summarize BlockedCount = count() by SenderDomain
| top 10 by BlockedCount
```
A security analyst runs the above KQL query in Microsoft 365 Defender. What is the primary purpose of this query?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Exhibit
Refer to the exhibit.
```kql
EmailEvents
| where Timestamp > ago(7d)
| where EmailDirection == "Inbound"
| where DeliveryAction == "Blocked"
| summarize BlockedCount = count() by SenderDomain
| top 10 by BlockedCount
```
A
Show the number of phishing clicks per user.
Why wrong: This option is incorrect because the query is analyzing `EmailEvents`, which contains email flow data, not phishing click data (which would be from `EmailUrlInfo` or `EmailClickAction`).
B
Identify the top 10 sender domains that were blocked in the last week.
Why wrong: This option is incorrect because the query does not filter by action type (e.g., 'Block'); it filters by authentication failure, not block actions.
C
List all emails that were allowed despite containing malware.
Why wrong: This option is incorrect because the query does not filter by action type 'Allow' or check for malware detection; it focuses on authentication failures.
D
Count emails that failed SPF/DKIM/DMARC.
This option is correct because the query filters for failed SPF/DKIM/DMARC authentication results and then counts the number of emails from each sender domain in the last week, displaying the top 10.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Count emails that failed SPF/DKIM/DMARC.
The KQL query uses `EmailEvents` with a filter on `EmailAuthenticationResult` for failed authentication (e.g., `where AuthenticationResult == 'Fail'`), then summarizes by `SenderMailFromDomain`, counts, sorts descending, and takes the top 10. The `where Timestamp > ago(7d)` restricts to the last week. Thus, the query identifies the top 10 sender domains that failed SPF/DKIM/DMARC in the last week.
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.
✗
Show the number of phishing clicks per user.
Why it's wrong here
This option is incorrect because the query is analyzing `EmailEvents`, which contains email flow data, not phishing click data (which would be from `EmailUrlInfo` or `EmailClickAction`).
✗
Identify the top 10 sender domains that were blocked in the last week.
Why it's wrong here
This option is incorrect because the query does not filter by action type (e.g., 'Block'); it filters by authentication failure, not block actions.
✗
List all emails that were allowed despite containing malware.
Why it's wrong here
This option is incorrect because the query does not filter by action type 'Allow' or check for malware detection; it focuses on authentication failures.
✓
Count emails that failed SPF/DKIM/DMARC.
Why this is correct
This option is correct because the query filters for failed SPF/DKIM/DMARC authentication results and then counts the number of emails from each sender domain in the last week, displaying the top 10.
Clue confirmation
The clue word "primary" 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 is that candidates may think the query counts all emails regardless of action, but the query includes a filter for blocked actions, so it specifically identifies blocked sender domains.
Detailed technical explanation
How to think about this question
The `EmailEvents` table in Microsoft 365 Defender Advanced Hunting contains one row per email event, including delivery actions like `Delivered`, `Blocked`, or `Junked`. The query `summarize Count = count() by SenderMailFromDomain` aggregates all events regardless of action, so it shows the most active sender domains in the environment. In a real-world scenario, a security analyst might use this to identify domains that are sending high volumes of email, which could indicate a spam campaign or a compromised sender, and then investigate further with additional filters.
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-900 question in full detail.
Describe Microsoft 365 apps and services — This question tests Describe Microsoft 365 apps and services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Count emails that failed SPF/DKIM/DMARC. — The KQL query uses `EmailEvents` with a filter on `EmailAuthenticationResult` for failed authentication (e.g., `where AuthenticationResult == 'Fail'`), then summarizes by `SenderMailFromDomain`, counts, sorts descending, and takes the top 10. The `where Timestamp > ago(7d)` restricts to the last week. Thus, the query identifies the top 10 sender domains that failed SPF/DKIM/DMARC in the last week.
What should I do if I get this MS-900 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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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