This post is a part of the AB-900: Microsoft 365 Copilot and Agent Administration Fundamentals Exam Prep Hub.
This topic falls under these sections:
Identify the core features and objects of Microsoft 365 services (30–35%)
   --> Identify the core objects of Microsoft 365 services
      --> Identify the appropriate objects to configure by using the Exchange Online Admin Center (mailboxes and distribution lists)

Note that there are 10 practice questions (with answers) at the end of each section to help you solidify your knowledge of the material. Also, there are 4 practice tests with 30 questions each available from the hub's main page below the exam topics section.

Introduction

Exchange Online is Microsoft’s cloud-based email and calendaring service that is part of Microsoft 365. It provides organizations with email, contacts, calendars, and collaboration capabilities without requiring on-premises email servers.

The Exchange admin center (EAC) is the primary portal used to manage Exchange Online objects and settings. For the AB-900: Microsoft 365 Copilot and Agent Administration Fundamentals exam, administrators should understand the common Exchange Online objects they manage, especially:

• Mailboxes
• Distribution lists (distribution groups)

These objects support communication and collaboration across the organization and are frequently used by Microsoft 365 services and Microsoft 365 Copilot.

What Is the Exchange Admin Center?

The Exchange admin center (EAC) is a web-based administrative portal used to manage Exchange Online.

Administrators can use the EAC to:

• Create and manage mailboxes.
• Manage distribution groups.
• Configure mail flow settings.
• Manage shared mailboxes.
• Configure permissions.
• Manage contacts and recipients.
• Troubleshoot email delivery.

The Exchange admin center focuses specifically on email and messaging services.

Understanding Exchange Online Recipients

In Exchange Online, objects that can send or receive email are called recipients.

Common recipient types include:

• User mailboxes
• Shared mailboxes
• Resource mailboxes
• Distribution groups
• Mail contacts
• Microsoft 365 Groups

For the AB-900 exam, the primary focus is understanding mailboxes and distribution lists.

User Mailboxes

A user mailbox belongs to an individual user.

It stores:

• Email messages
• Calendar items
• Contacts
• Tasks

Each licensed user normally receives a mailbox.

Example

jane@contoso.com

A user mailbox is associated with:

• A Microsoft Entra ID account
• A Microsoft 365 license
• Exchange Online services

Characteristics of User Mailboxes

User mailboxes provide:

• Personal email storage
• Calendar scheduling
• Contact management
• Integration with Outlook and Teams
• Support for Microsoft 365 Copilot experiences

Each mailbox is private to the assigned user unless permissions are granted.

Shared Mailboxes

A shared mailbox allows multiple users to read and send email from a common address.

Examples:

support@contoso.com
sales@contoso.com
info@contoso.com

Multiple employees can:

• Read incoming messages.
• Reply as the shared mailbox.
• Manage the mailbox together.

Benefits of Shared Mailboxes

Shared mailboxes are commonly used for:

Department Email

Example:

hr@contoso.com

Customer Service Teams

Example:

helpdesk@contoso.com

General Company Inquiries

Example:

info@contoso.com

Shared mailboxes improve collaboration and prevent messages from being tied to one individual.

Resource Mailboxes

Resource mailboxes represent resources rather than people.

Two common types are:

Room Mailboxes

Represent meeting rooms.

Example:

ConferenceRoom1@contoso.com

Equipment Mailboxes

Represent shared equipment.

Example:

Projector1@contoso.com

These mailboxes support scheduling and booking.

Distribution Lists (Distribution Groups)

A distribution list (distribution group) is an email-enabled group that sends a single message to multiple recipients.

Example:

AllSales@contoso.com

Sending one message to the group automatically delivers it to all members.

Purpose of Distribution Lists

Distribution groups simplify communication by allowing administrators and users to:

• Send announcements.
• Communicate with departments.
• Reach project teams.
• Avoid entering individual addresses.

Examples:

Characteristics of Distribution Groups

Distribution groups:

• Are email-enabled.
• Do not have their own mailbox.
• Deliver messages to all members.
• Can contain users and other groups.
• Simplify communication.

A distribution group is different from a shared mailbox because it does not store email.

Dynamic Distribution Groups

A dynamic distribution group automatically determines membership using recipient attributes.

Examples of attributes:

• Department
• Office location
• Company
• Job title

Example

Rule:

Department = Sales

When a new salesperson joins the organization, they automatically become part of the group.

Dynamic distribution groups reduce administrative effort.

Microsoft 365 Groups vs Distribution Groups

Although they both support email communication, they serve different purposes.

Distribution groups are designed primarily for email distribution.

Mail Contacts

A mail contact represents an external email address.

Example:

vendor@example.com

The contact appears in the organization’s address book but does not have a mailbox in the tenant.

Managing Mailboxes in the Exchange Admin Center

Administrators can perform tasks such as:

• Create mailboxes.
• Modify email addresses.
• Assign permissions.
• Convert mailboxes.
• Configure forwarding.
• Manage storage settings.

These actions are performed under the Recipients → Mailboxes section of the Exchange admin center.

Managing Distribution Lists

Administrators can:

• Create groups.
• Add or remove members.
• Modify group owners.
• Change email addresses.
• Configure delivery restrictions.

These tasks are performed under:

Recipients → Groups

Mailbox Permissions

Administrators may assign permissions to allow users to access another mailbox.

Common permissions include:

Full Access

Allows a user to open and view another mailbox.

Send As

Allows a user to send email appearing to come from another mailbox.

Example:

A user sends email as:

support@contoso.com

Send on Behalf

Recipients see both the sender and mailbox owner.

Example:

John on behalf of Support Team

Mail Flow and Email Delivery

Exchange Online manages:

• Sending email.
• Receiving email.
• Message routing.
• Delivery between users.

Distribution groups and mailboxes participate in this mail flow system.

Why Exchange Online Objects Matter for Microsoft 365 Copilot

Microsoft 365 Copilot can use information stored in Exchange Online, including:

• Emails
• Calendars
• Meeting information

Properly configured mailboxes help Copilot provide relevant responses while respecting existing user permissions.

Copilot only accesses content that users are already authorized to access.

Best Practices

Use Shared Mailboxes for Team Communication

Avoid using personal accounts for department email.

Use Distribution Groups for Broadcast Messaging

Distribution groups simplify communications to large audiences.

Use Dynamic Distribution Groups When Possible

Automatic membership reduces administrative overhead.

Assign Permissions Carefully

Grant only the access users require.

Maintain Accurate Membership Lists

Outdated groups can result in communication errors.

Exam Tips

Remember these AB-900 concepts:

• User mailboxes belong to individual users.
• Shared mailboxes are used by multiple users.
• Resource mailboxes represent rooms and equipment.
• Distribution groups distribute email to many recipients.
• Distribution groups do not store email.
• Dynamic distribution groups automatically determine membership.
• Mail contacts represent external addresses.
• Exchange Online objects are managed through the Exchange admin center.
• Microsoft 365 Groups provide additional collaboration capabilities beyond email.

Practice Exam Questions

Question 1

Which Exchange Online object stores email, calendar items, contacts, and tasks for an individual user?

A. Distribution group
B. Shared mailbox
C. User mailbox
D. Mail contact

Correct Answer: C

Explanation: A user mailbox is assigned to a specific person and stores their email and related information.

Question 2

A company wants several employees to manage emails sent to:

support@contoso.com

Which object should be used?

A. Shared mailbox
B. Dynamic distribution group
C. Mail contact
D. Resource mailbox

Correct Answer: A

Explanation: Shared mailboxes allow multiple users to access and respond to messages from a common email address.

Question 3

Which object is designed primarily to send one email message to multiple recipients?

A. Equipment mailbox
B. User mailbox
C. Distribution group
D. Shared mailbox

Correct Answer: C

Explanation: Distribution groups simplify communication by delivering one message to all members.

Question 4

Which statement about a distribution group is true?

A. It contains a personal calendar.
B. It stores email messages.
C. It automatically creates a SharePoint site.
D. It forwards messages to its members.

Correct Answer: D

Explanation: Distribution groups do not store mail; they distribute incoming messages to group members.

Question 5

What type of mailbox represents a conference room?

A. Shared mailbox
B. User mailbox
C. Distribution group
D. Room mailbox

Correct Answer: D

Explanation: Room mailboxes represent meeting spaces and support scheduling.

Question 6

Which Exchange Online object can automatically include users based on attributes such as department?

A. Shared mailbox
B. Mail contact
C. Dynamic distribution group
D. Equipment mailbox

Correct Answer: C

Explanation: Dynamic distribution groups determine membership automatically using recipient properties.

Question 7

What is the primary purpose of a mail contact?

A. Provide external email addresses in the organization’s address book
B. Store shared emails
C. Manage conference rooms
D. Create Teams workspaces

Correct Answer: A

Explanation: Mail contacts represent recipients outside the organization and do not have internal mailboxes.

Question 8

Which mailbox permission allows a user to send messages that appear to come directly from another mailbox?

A. Full Access
B. Send As
C. Send on Behalf
D. Owner

Correct Answer: B

Explanation: Send As permission allows messages to appear as though they originated from the mailbox itself.

Question 9

Where in the Exchange admin center are mailbox objects typically managed?

A. Mail flow → Rules
B. Protection → Policies
C. Recipients → Mailboxes
D. Organization → Sharing

Correct Answer: C

Explanation: The Recipients → Mailboxes section is used to manage mailbox objects.

Question 10

Which capability is available with Microsoft 365 Groups but not traditional distribution groups?

A. Email delivery
B. Membership management
C. External contacts
D. Shared collaboration resources such as SharePoint sites

Correct Answer: D

Explanation: Microsoft 365 Groups provide additional collaboration resources, including shared mailboxes, calendars, SharePoint sites, and Teams integration.

Go to the AB-900 Exam Prep Hub main page