Archive Mailboxes

Enable and manage in-place archive mailboxes for Exchange Online users. Archive mailboxes provide additional storage for historical email content, helping users maintain clean primary mailboxes while retaining important messages.

Note: Archive mailboxes require Exchange Online Plan 2, or Exchange Online Plan 1 with an Exchange Online Archiving add-on. Microsoft 365 E3 and E5 plans include archiving.

Archive Mailbox List

How Archive Mailboxes Work

1. Enable Archive — Administrator enables in-place archive for a user mailbox.
2. Retention Policy — Retention tags move items older than a specified age to the archive.
3. User Access — Users can access archive via Outlook desktop and Outlook on the web.
4. Search — Archive content is included in eDiscovery and compliance searches.

Auto-Expanding Archive

When a user archive mailbox reaches capacity, Exchange Online automatically provisions additional storage space.

• Storage is added in 50 GB increments
• Maximum capacity grows up to 1.5 TB
• Must be enabled by an administrator at the organization level
• Cannot be disabled once enabled for a mailbox
• Applies to both active and inactive mailboxes

Warning: Auto-expanding archive cannot be reversed once enabled. Ensure your organization is committed to this storage model before turning it on.

Retention Policies for Archiving

Configure retention policies to automatically move items to the archive:

Default MRM Policy

Exchange Online includes a Default MRM Policy with archive tags:

• Default 2 year move to archive — Moves all items older than 2 years to archive
• Personal 1 year move to archive — Users can apply to folders or items
• Personal 5 year move to archive — Longer retention before archive move
• Personal never move to archive — Exempt items from archiving

Custom Archive Tags

Create custom retention tags for specific needs:

• Default Policy Tag (DPT) — Applies to all items not covered by other tags
• Retention Policy Tag (RPT) — Applies to specific default folders (Inbox, Sent, etc.)
• Personal Tag — Users apply manually to items or folders

Enabling Archive Mailboxes

1. Select User — Choose the mailbox to enable archive for.
2. Enable Archive — Turn on the in-place archive.
3. Assign Policy — Apply a retention policy with archive move tags.
4. Verify — Confirm archive appears in user Outlook within 24 hours.

Note: The Managed Folder Assistant processes mailboxes within 7 days. To expedite, run Start-ManagedFolderAssistant in PowerShell.

Archive Access

Outlook Desktop

Archive mailbox appears as “Online Archive - username” in the folder pane. Full read/write access to archived items.

Outlook on the Web

Archive accessible from the folder list. Supports search, move, and delete operations on archived content.

Outlook Mobile

Limited archive access on mobile devices. Users can search archive content but may not see the archive folder directly.

Best Practices

• Enable auto-expanding archive — Prevents archive quota issues for high-volume users.
• Use retention policies — Automate the archiving process rather than relying on manual moves.
• Monitor archive sizes — Track archive growth to plan for storage needs.
• Train users — Educate users on how to access and search their archive in Outlook.

API Reference

GET /api/exchange/archive-mailboxes List archive mailbox status for all users

POST /api/exchange/archive-mailboxes/:mailboxId/enable Enable archive mailbox

GET /api/exchange/archive-mailboxes/:mailboxId/statistics Get archive mailbox size and item count

PUT /api/exchange/archive-mailboxes/auto-expanding Enable auto-expanding archive organization-wide