1. Install the Exchange Online PowerShell Module on your computer

Open PowerShell as Administrator and run:
Install-Module -Name ExchangeOnlineManagement

You may be prompted to trust the repository. Type Y to proceed.

2. Import the Module

Import-Module ExchangeOnlineManagement

3. Connect to Exchange Online

Connect-ExchangeOnline -UserPrincipalName 

Replace <UserPrincipalName> with your admin email (e.g., admin@contoso.com). You’ll be prompted to sign in.

4. Enable Auto-Expanding Archive

For the organization:
Set-OrganizationConfig -AutoExpandingArchive 

For a specific user:
Enable-Mailbox <user mailbox> -AutoExpandingArchive

5. Verify Auto-Expanding Archive Status

Organization-wide:
Get-OrganizationConfig | FL AutoExpandingArchiveEnabled

Specific user:
Get-Mailbox <user mailbox> | FL AutoExpandingArchiveEnabled
 
 Important Considerations

• Auto-expanding archive cannot be disabled once enabled.
• Expansion begins only after the archive mailbox reaches 90 GB and may take up to 30 days.
• Not supported for mailboxes used for journaling or auto-forwarding.