Microsoft Entra ID Interview Questions and Answers – Part 3: Domains

SECTION E — Domains

Q43. What is a Microsoft Entra ID Domain?

A Microsoft Entra ID domain is a domain name that is associated with a Microsoft Entra tenant and can be used as part of users’ sign-in names, email addresses, and other identity-related configurations.

A tenant can have an initial domain provided by Microsoft and can also have one or more custom domains added by the organization.

For example:

Microsoft Entra Tenant
        │
        ├── Initial domain
        │     └── abccompany.onmicrosoft.com
        │
        └── Custom domain
              └── abccompany.com

What is an Initial Domain?

When a Microsoft Entra tenant is created, Microsoft provides an initial domain ending in:

.onmicrosoft.com

For example:

abccompany.onmicrosoft.com

This domain is associated with the tenant and is available for use even if the organization has not yet added its own custom domain.

The initial domain is useful when setting up the tenant and creating initial users and identities.

What is a Custom Domain?

An organization can add its own domain to Microsoft Entra ID.

For example, instead of users signing in with:

john@abccompany.onmicrosoft.com

the organization may configure:

john@abccompany.com

Here:

abccompany.com is the organization’s custom domain.

Custom domains make the Microsoft cloud identity environment align with the organization’s existing business identity and email domain.

Q44. Why do organizations add custom domains?

Suppose a company called ABC Corporation owns:

abccompany.com

When the company first creates its Microsoft Entra tenant, it may receive:

abccompany.onmicrosoft.com

However, the organization probably wants employees to use:

john@abccompany.com

rather than:

john@abccompany.onmicrosoft.com

Adding and verifying the organization’s custom domain allows the company to use its own domain for identities.

This provides a more familiar and professional sign-in experience.

Q45. Can a tenant have multiple domains?

Yes.

A Microsoft Entra tenant can have multiple domain names associated with it.

For example:

ABC Corporation – Microsoft Entra Tenant
│
├── abccompany.onmicrosoft.com
├── abccompany.com
├── abccompany.co.uk
└── subsidiary.com

This can be useful for organizations that operate with:

• Multiple business domains
• Different brands
• Subsidiaries
• Different geographic regions
• Multiple email namespaces

However, adding a domain to a tenant does not automatically mean that every user will use that domain.

Administrators can assign appropriate domain names when creating or configuring identities.

Q46. How is a Custom Domain Added?

At a high level, the process is:

Organization owns abccompany.com
              ↓
Add abccompany.com to Entra ID
              ↓
Microsoft provides verification information
              ↓
Add required DNS record
              ↓
Verify ownership
              ↓
Domain becomes verified
              ↓
Domain can be used in Entra ID

Microsoft requires domain ownership verification before a custom domain can be used as a verified domain in the tenant.

The exact DNS record and administration steps can vary depending on the verification method and Microsoft’s current portal experience.

Q47. Difference between Domain vs Tenant

A domain should not be confused with a tenant.

For example:

Tenant:
ABC Corporation's Microsoft Entra environment

Tenant ID:
12345678-abcd-1234-abcd-123456789abc

Domains:
abccompany.onmicrosoft.com
abccompany.com

The tenant is the identity environment.

The domains are names associated with that tenant.

A tenant can therefore have multiple domains.

Q48. Difference between Domain vs Email Address

Another common source of confusion is the difference between a domain and a user’s email/sign-in address.

For example:

john@abccompany.com

can be broken into:

Username: john

Domain: abccompany.com

The domain itself is not the user account.

It is the namespace used as part of the user’s identity.

Real-World Example

Imagine a company called Contoso Technologies.

When it creates a Microsoft Entra tenant, it might receive:

contoso123.onmicrosoft.com

The company already owns:

contoso.com

The administrator adds and verifies contoso.com in Microsoft Entra ID.

The organization can then use identities such as:

john@contoso.com

admin@contoso.com

rather than relying solely on the initial onmicrosoft.com domain.

The tenant remains the same.

Only the domain namespace being used for identities has been added.

⚠️ Common Interview Mistakes

Mistake 1:

“The custom domain is the Microsoft Entra tenant.”

❌ Incorrect.

The domain is associated with the tenant.

Mistake 2:

“Every tenant can have only one domain.”

❌ Incorrect.

A tenant can have multiple associated domains.

Mistake 3:

“Adding a custom domain automatically migrates users.”

❌ Incorrect.

Adding and verifying a domain does not automatically migrate all identities or change every user’s sign-in address.

Mistake 4:

“The .onmicrosoft.com domain is optional.”

The tenant receives an initial onmicrosoft.com domain as part of tenant creation. Organizations can add custom domains in addition to it.

🎯 Interview Tip

If asked:

“What is a Microsoft Entra ID domain?”

A strong answer would be:

“A Microsoft Entra ID domain is a domain name associated with a Microsoft Entra tenant. A tenant receives an initial onmicrosoft.com domain when it is created, and an organization can add and verify custom domains such as company.com for user sign-in names and other identity-related purposes.”

If the interviewer asks:

“Can one tenant have multiple domains?”

Answer:

“Yes. A Microsoft Entra tenant can have multiple associated domains, including the initial onmicrosoft.com domain and one or more verified custom domains.”

Quick Revision

Tenant = Identity environment

Domain = Namespace associated with the tenant

Initial domain = onmicrosoft.com

Custom domain = Organization’s own domain, such as company.com

And remember:

One Microsoft Entra tenant can have multiple domains.

Q49. What is the default onmicrosoft.com domain in Microsoft Entra ID?

When a Microsoft Entra tenant is created, Microsoft provides an initial domain that ends with:

.onmicrosoft.com

For example:

contoso.onmicrosoft.com

This initial domain is automatically associated with the tenant and can be used for identities and other tenant-related purposes.

It provides an organization with a usable domain namespace before it adds and verifies its own custom domain.

Simple example

Suppose a company called ABC Corporation creates a Microsoft Entra tenant.

During tenant creation, it may receive an initial domain such as:

abccompany.onmicrosoft.com

The organization can then have a user such as:

john@abccompany.onmicrosoft.com

Later, the company can add and verify its own domain:

abccompany.com

The same tenant could then use:

john@abccompany.com

The important point is:

Adding a custom domain does not create a new tenant.

The custom domain is simply associated with the existing Microsoft Entra tenant.

Q50. Why does Microsoft provide an onmicrosoft.com domain?

The initial domain gives the tenant a Microsoft-managed namespace immediately after the tenant is created.

This is useful because an organization may not have configured its own domain yet.

For example:

New Microsoft Entra Tenant
          │
          ▼
Initial domain assigned
          │
          ▼
companyname.onmicrosoft.com
          │
          ▼
Users and tenant configuration
          │
          ▼
Optional custom domain
          │
          ▼
company.com

The organization can therefore start configuring its Microsoft cloud environment before adding a custom domain.

Q51. Can the onmicrosoft.com domain be removed?

The initial domain has a special role in the tenant and should not be treated like an ordinary custom domain.

An organization can add additional custom domains, but the initial onmicrosoft.com domain remains associated with the tenant.

Therefore, administrators should not think of the custom domain process as replacing the tenant’s underlying Microsoft-provided identity namespace.

Q52. Can users continue using the onmicrosoft.com domain?

Yes, depending on the organization’s configuration and requirements.

For example, a tenant might contain:

john@company.com
sarah@company.com
admin@company.onmicrosoft.com

However, organizations generally prefer their custom domain for employee-facing identities because it aligns with their corporate identity.

The onmicrosoft.com domain may still appear in administrative, technical, or tenant-related scenarios.

Q53. Is onmicrosoft.com the same as a custom domain?

No.

The distinction is:

Real-world example

Suppose XYZ Technologies creates a Microsoft Entra tenant.

Its initial domain might be:

xyztechnologies.onmicrosoft.com

The organization already owns:

xyztechnologies.com

The administrator adds and verifies:

xyztechnologies.com

The tenant can then use identities such as:

john@xyztechnologies.com

while the original:

xyztechnologies.onmicrosoft.com

remains associated with the tenant.

So the organization now has one tenant with multiple domains.

⚠️ Common Interview Mistakes

Mistake 1:

“onmicrosoft.com is the tenant.”

❌ Incorrect.

The onmicrosoft.com name is a domain associated with the tenant.

Mistake 2:

“Adding a custom domain creates another tenant.”

❌ Incorrect.

The custom domain is added to the existing tenant.

Mistake 3:

“The initial domain is the same as the company’s actual domain.”

Not necessarily.

The initial domain is provided through Microsoft’s tenant creation process, while the organization can later add its own verified domain.

🎯 Interview Tip

If asked:

“What is the onmicrosoft.com domain?”

A strong answer is:

“When a Microsoft Entra tenant is created, Microsoft provides an initial domain ending in onmicrosoft.com. It provides the tenant with an initial namespace that can be used for identities and tenant-related configuration. The organization can later add and verify custom domains such as company.com without creating a new tenant.”

Quick Revision

onmicrosoft.com = Initial Microsoft-provided domain associated with the tenant

company.com = Custom domain added and verified by the organization

And remember:

Adding a custom domain does not create a new Microsoft Entra tenant.

Q54. What is a Custom Domain in Microsoft Entra ID?

A custom domain in Microsoft Entra ID is an organization’s own domain name that is added to and verified within a Microsoft Entra tenant.

For example, Microsoft provides an initial domain such as:

contoso.onmicrosoft.com

If the organization owns:

contoso.com

it can add contoso.com as a custom domain to its Microsoft Entra tenant.

After the domain is verified, the organization can use it for identities and other supported Microsoft cloud scenarios.

Simple definition: A custom domain allows an organization to use its own domain name with its Microsoft Entra identity environment.

Q55. Why is domain verification required?

Microsoft needs to confirm that the organization actually owns or controls the domain before allowing it to be associated as a verified domain in the tenant.

For example, suppose an organization claims ownership of:

contoso.com

Another person should not be able to simply add contoso.com to their Microsoft Entra tenant.

Therefore, Microsoft provides a verification method involving a DNS record.

The administrator adds the required record to the organization’s DNS configuration.

Microsoft then checks the DNS information to verify control of the domain.

Q56. How does the custom-domain process work?

At a high level:

Organization owns
    contoso.com
        │
        ▼
Add domain to
Microsoft Entra ID
        │
        ▼
Microsoft provides
verification information
        │
        ▼
Add DNS verification
record
        │
        ▼
Microsoft verifies
domain ownership
        │
        ▼
Domain becomes
verified
        │
        ▼
Can be used in
supported scenarios

The exact DNS record and portal steps can change as Microsoft updates its services, so administrators should follow the current Microsoft documentation when performing the configuration.

Example

Imagine ABC Corporation owns:

abccompany.com

Its Microsoft Entra tenant initially has:

abccompany.onmicrosoft.com

The administrator adds:

abccompany.com

to the tenant.

Microsoft provides the required verification information.

The administrator adds the appropriate DNS record to the organization’s DNS provider.

After Microsoft verifies the domain:

Microsoft Entra Tenant
        │
        ├── abccompany.onmicrosoft.com
        │       Initial domain
        │
        └── abccompany.com
                Custom domain
                ✓ Verified

The organization can then use the custom domain for supported identity-related configurations.

For example, users can have sign-in names such as:

john@abccompany.com

instead of:

john@abccompany.onmicrosoft.com

Q57. Can a tenant have multiple custom domains?

Yes.

A Microsoft Entra tenant can have multiple verified custom domains.

For example:

ABC Corporation
       │
       ▼
Microsoft Entra Tenant
       │
       ├── abccompany.onmicrosoft.com
       ├── abccompany.com
       ├── abccompany.co.uk
       └── abcsubsidiary.com

This can be useful for organizations that have:

• Multiple business domains
• Subsidiaries
• Multiple brands
• Different geographic domains
• Different organizational namespaces

The exact design depends on the organization’s identity requirements.

Q58. Custom Domain vs Initial Domain

This distinction is important.

Both can coexist in the same tenant.

Q59. Does adding a custom domain automatically change existing users?

Not necessarily.

Adding and verifying a custom domain does not automatically mean every existing user’s sign-in name is changed.

For example, if a user currently has:

john@abccompany.onmicrosoft.com

adding:

abccompany.com

doesn’t automatically mean the user becomes:

john@abccompany.com

The administrator must configure the appropriate identity properties according to the organization’s requirements.

This is an important distinction in real-world administration.

Q60. Does a Custom Domain Create a New Tenant?

No.

This is one of the most important points to remember.

Suppose you already have:

Tenant:
ABC Corporation

Tenant ID:
12345678-abcd-1234-abcd-123456789abc

and you add:

abccompany.com

You still have:

One Microsoft Entra tenant

You have simply added another verified domain to that tenant.

⚠️ Common Interview Mistakes

Mistake 1:

“A custom domain is the same thing as a tenant.”

❌ Incorrect.

A custom domain is associated with a tenant.

Mistake 2:

“You can add any domain without verification.”

❌ Incorrect.

Microsoft requires domain verification to establish control of the domain.

Mistake 3:

“Adding a custom domain automatically changes every user’s username.”

❌ Incorrect.

Adding the domain and changing user identities are separate administrative actions.

Mistake 4:

“One tenant can have only one domain.”

❌ Incorrect.

A tenant can have multiple associated domains, subject to Microsoft’s current service limits and configuration rules.

🎯 Interview Tip

If asked:

“What is a custom domain in Microsoft Entra ID?”

A strong answer is:

“A custom domain is an organization’s own domain that is added to and verified within a Microsoft Entra tenant. For example, an organization can add company.com to its tenant and use it for supported identity-related scenarios. Microsoft requires domain verification, typically through DNS, to confirm that the organization controls the domain.”

If the interviewer asks:

“Does adding a custom domain create a new tenant?”

Answer:

“No. The custom domain is added to the existing Microsoft Entra tenant. It does not create a new tenant.”

Quick Revision

Custom Domain = Organization’s own domain added to Microsoft Entra ID

Example:

Initial domain: company.onmicrosoft.com

Custom domain: company.com

Remember:

Add → Verify → Configure → Use

Q61. Why Would an Organization Add a Custom Domain to Microsoft Entra ID?

Organizations add a custom domain to Microsoft Entra ID so that they can use their own organizational domain name for identities and supported Microsoft cloud services.

For example, instead of using:

john@contoso.onmicrosoft.com

an organization may want its users to use:

john@contoso.com

A custom domain provides a more familiar identity experience and allows the organization’s Microsoft cloud identities to align with its existing business domain.

1. To Use the Organization’s Existing Domain

Most organizations already own a domain name.

For example:

contoso.com

After adding and verifying this domain in Microsoft Entra ID, the organization can use it within its Microsoft cloud identity environment.

Organization's existing domain
          │
          ▼
      contoso.com
          │
          ▼
Add to Microsoft Entra ID
          │
          ▼
Verify ownership
          │
          ▼
Use for supported
identity scenarios

This allows the organization’s cloud identities to use a familiar corporate namespace.

2. To Provide a Professional Sign-In Experience

Compare:

Without custom domain:

john@contoso.onmicrosoft.com

With custom domain:

john@contoso.com

The second address is generally easier for employees, customers, and partners to recognize as belonging to the organization.

For companies already using contoso.com for email and other services, using the same domain for Microsoft Entra identities provides a more consistent identity experience.

3. To Align Microsoft 365 with the Organization’s Identity

Microsoft Entra ID is closely integrated with Microsoft 365.

An organization may already use its custom domain for services such as:

• Corporate email
• Company website
• User identities
• Microsoft 365
• Other business applications

Using the organization’s domain in Microsoft Entra ID helps maintain a consistent identity namespace.

For example:

                 contoso.com
                      │
       ┌──────────────┼──────────────┐
       ▼              ▼              ▼
   Microsoft       Email         Business Apps
   Entra ID
       │
       ▼
   Microsoft 365

4. To Support Multiple Business Domains

Large organizations may have more than one domain.

For example:

Microsoft Entra Tenant
       │
       ├── contoso.com
       ├── contoso.co.uk
       ├── contoso.de
       └── subsidiary.com

Different domains may represent:

• Different countries
• Different brands
• Subsidiaries
• Acquired companies
• Different business units

Microsoft Entra ID allows organizations to associate multiple domains with a tenant.

5. To Make User Sign-In Names Easier to Understand

A custom domain can make users’ sign-in names more recognizable.

For example:

john@contoso.com

is immediately recognizable as a corporate identity.

This can also make administrative tasks easier because administrators can quickly identify which organization or domain a user belongs to.

6. To Support Existing Identity and Email Naming Conventions

Organizations often have established naming standards.

For example:

firstname.lastname@contoso.com

When Microsoft cloud identities are configured, the organization may want to maintain the same naming convention.

This can provide consistency across:

• Microsoft Entra ID
• Microsoft 365
• Exchange Online
• Other applications

The exact configuration depends on the organization’s environment.

Important: A Custom Domain Does Not Replace the Tenant

Adding a custom domain does not create a new Microsoft Entra tenant.

For example:

Microsoft Entra Tenant
       │
       ├── contoso.onmicrosoft.com
       │
       └── contoso.com

There is still only one tenant.

The organization has simply added another verified domain to that tenant.

Q62. Difference between Custom Domain vs Tenant

This distinction is worth remembering for interviews.

Tenant = Identity environment

Custom domain = Domain namespace associated with the tenant

For example:

Tenant: Contoso’s Microsoft Entra environment

Tenant ID: 12345678-abcd-1234-abcd-123456789abc

Custom domain: contoso.com

They are three different concepts.

⚠️ Common Interview Mistakes

Mistake 1:

“The custom domain is required to create a Microsoft Entra tenant.”

❌ Incorrect.

A tenant receives an initial Microsoft-provided domain when it is created.

Mistake 2:

“Adding a custom domain creates another tenant.”

❌ Incorrect.

It is added to the existing tenant.

Mistake 3:

“Custom domains are only used for email.”

❌ Incorrect.

They can be used for supported Microsoft Entra identity and Microsoft cloud scenarios; they are not simply an email feature.

🎯 Interview Tip

If asked:

“Why would an organization add a custom domain to Microsoft Entra ID?”

A strong answer would be:

“Organizations add a custom domain so they can use their own verified domain, such as company.com, with their Microsoft Entra environment. This provides a consistent and recognizable identity namespace, supports organizational naming conventions, and can accommodate multiple business domains. The custom domain is added to the existing tenant; it does not create a new tenant.”

🔗 Related Interview Questions

Continue Learning :

• Q63. What is a Microsoft Entra ID User?
• Q67. Difference between Cloud-only User vs Synchronized User
• Q70. What happens when a user is disabled?

Quick Revision

Organizations add custom domains mainly to:

Use their own domain → Provide recognizable identities → Maintain naming consistency → Support multiple organizational domains

Example:

john@contoso.com

instead of:

john@contoso.onmicrosoft.com