Microsoft 365 Mailbox

What is Microsoft 365 Mailbox?

A Microsoft 365 Mailbox refers to a cloud-hosted mailbox provided as part of Microsoft 365’s Exchange Online service. It enables users to send, receive, and manage emails, along with access to calendaring, contacts, and tasks. Each user with an assigned license typically gets their own mailbox, which is accessible from anywhere via Outlook, web, or mobile apps.

Are Microsoft 365 Mailboxes Free?

Microsoft 365 mailboxes are not completely free. While basic Outlook functionality may be available with a free Microsoft account (e.g., Outlook.com), Microsoft 365 Mailboxes with enterprise-grade features—such as 50GB+ storage, shared mailboxes, and compliance tools—require a paid Microsoft 365 subscription, such as Business Basic, Standard, or Office 365 E1/E3/E5 plans.

Key Features of Microsoft 365 Mailboxes

• Mailbox Storage Limits:
• Business Basic & Standard: 50 GB
• Exchange Online Plan 2 & E3/E5: 100 GB
• Archive mailbox (Auto-Expanding Archive): Starts at 100 GB, expandable based on usage.
• Mailbox Retention Policy:
• Default retention policies can retain deleted emails for 14 to 30 days.
• Administrators can configure policies using Microsoft Purview or Security & Compliance Center for legal hold and compliance.
• Mailbox Permissions:
• Full Access: Read, write, and delete messages.
• Send As: Send email as the mailbox owner.
• Send on Behalf: Send messages on behalf of another user.
• Advanced Features:
• Focused Inbox, Clutter control, Anti-phishing & malware protection, M365 eDiscovery, and mail flow rules.

Different Ways of Creating Microsoft 365 Mailboxes

1. Using Microsoft 365 Admin Center

When you assign a license (that includes Exchange Online) to a user, a mailbox is automatically provisioned.

2. Using Exchange Admin Center (EAC)

Admins can create mailboxes under Recipients > Mailboxes, including shared and resource mailboxes.

3. Using Exchange PowerShell

New-Mailbox -UserPrincipalName "john.doe@contoso.com" -Alias "johndoe"

4. Using Microsoft Graph PowerShell

For automation:

$params = @{
    accountEnabled = $true
    displayName = "John Doe"
    mailNickname = "johndoe"
    userPrincipalName = "john.doe@contoso.com"
    passwordProfile = @{ forceChangePasswordNextSignIn = $true; password = "xWwvJ]6NMw+bWH-d" }
}
New-MgUser -BodyParameter $params
                                            

Note: Graph doesn't directly create a mailbox, but provisioning a user with an Exchange license triggers mailbox creation.

Summary

Key Point	Details
Feature Name	Microsoft 365 Mailbox
Purpose	Cloud-based email, calendaring, and collaboration
Included In	Business Basic/Standard, Office 365 E1/E3/E5, Education A1/A3/A5
Free to Use?	Only with assigned license; no standalone free business mailboxes
Access Method	office.com, Outlook apps, Admin Center, Microsoft365.com
Integrates With	Teams, OneDrive, Outlook, Microsoft Graph, Power Automate, Viva