Quick Answer
The answer is user@contoso.onmicrosoft.com. This default email address format for a new tenant is set because when you create a Microsoft 365 tenant, Azure AD automatically provisions an onmicrosoft.com domain as the initial namespace, and all user principal names (UPNs) and email addresses inherit this suffix until a custom domain is verified and set as primary. On the MS-102 exam, this concept tests your understanding of tenant provisioning and domain management, often appearing in scenario-based questions where candidates must distinguish between the default onmicrosoft.com format and custom domain configurations. A common trap is assuming the email address can use a custom domain before it is verified, so remember that the tenant’s initial domain is always the onmicrosoft.com suffix. Memory tip: think of “onmicrosoft” as the tenant’s birth name—it stays until you add a custom alias.
This MS-102 practice question tests your understanding of deploy and manage a microsoft 365 tenant. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 organization has just signed up for Microsoft 365 E3 with the initial domain 'contoso.onmicrosoft.com'. They need to create the first user accounts. What will be the default email address format for these new users if no custom domain is added yet?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
user@contoso.onmicrosoft.com
The default domain is the onmicrosoft.com domain assigned during tenant creation.
user@contoso.com
Why wrong: This would require a custom domain to be added and set as default.
user@microsoft.com
Why wrong: Microsoft.com is not related to the tenant's domain.
user@contoso.microsoft.com
Why wrong: This is not a valid default domain format for Microsoft 365 tenants.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
user@contoso.onmicrosoft.com
When a new Microsoft 365 tenant is created with the initial domain 'contoso.onmicrosoft.com' and no custom domain has been added, the default email address format for new users is user@contoso.onmicrosoft.com. This is because the onmicrosoft.com domain is the default tenant domain provisioned by Azure AD, and all user principal names (UPNs) and email addresses are automatically assigned this suffix until a custom domain is verified and set as the primary domain.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
user@contoso.onmicrosoft.com
Why this is correct
The default domain is the onmicrosoft.com domain assigned during tenant creation.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
user@contoso.com
Why it's wrong here
This would require a custom domain to be added and set as default.
user@microsoft.com
Why it's wrong here
Microsoft.com is not related to the tenant's domain.
user@contoso.microsoft.com
Why it's wrong here
This is not a valid default domain format for Microsoft 365 tenants.
Common exam traps
The trap here is that candidates assume the email address will automatically match the organization's public domain name (e.g., contoso.com) without realizing that a custom domain must be explicitly added and verified in the Microsoft 365 admin center before it can be used for user email addresses.
Detailed technical explanation
Under the hood, the onmicrosoft.com domain is registered as the initial Azure AD domain with a unique tenant ID, and the UPN for each user is constructed as <username>@<tenantname>.onmicrosoft.com. This domain cannot be removed or changed; it persists even after custom domains are added, and it is used for internal routing and as a fallback for authentication. In real-world scenarios, organizations often keep this domain for admin accounts or break-glass accounts to avoid dependency on custom domain DNS availability.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
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..
The correct answer is: user@contoso.onmicrosoft.com — When a new Microsoft 365 tenant is created with the initial domain 'contoso.onmicrosoft.com' and no custom domain has been added, the default email address format for new users is user@contoso.onmicrosoft.com. This is because the onmicrosoft.com domain is the default tenant domain provisioned by Azure AD, and all user principal names (UPNs) and email addresses are automatically assigned this suffix until a custom domain is verified and set as the primary domain.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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