This chapter covers archiving and In-Place Archive in Exchange Online, a key component of Microsoft 365's compliance and storage management capabilities. For the MS-900 exam, this topic falls under Domain 3: Security, Compliance, Privacy, and Trust, specifically objective 3.4: 'Describe the compliance management capabilities in Microsoft 365.' Expect 2-3 questions that test your understanding of archive mailbox features, retention policies, and how archiving integrates with broader compliance tools like litigation hold and eDiscovery. Mastering this chapter will help you differentiate between archiving, backup, and retention, and understand the default and configurable limits that appear on the exam.
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Imagine a busy law office where every attorney has a desk with a filing cabinet. The cabinet holds current cases—documents they access daily. Over time, the cabinet fills up, so the office manager installs a secondary, larger filing cabinet in the basement. This basement cabinet is the In-Place Archive. The manager sets a policy: any file not touched in 30 days automatically gets moved to the basement cabinet. The attorney still sees the file in their desktop index—they can open it with a double-click—but the physical paper now resides in the basement. If a client visits, the attorney doesn't need to fetch from the basement every time; the index shows a placeholder. Only when they actually try to open the file does the system retrieve it from the basement. The basement cabinet has a much larger capacity—say 50 GB per attorney—and is cheaper per page than the desk cabinet. The office manager can also set rules: emails with 'Confidential' in the subject go directly to the basement. This mirrors Exchange Online's In-Place Archive: a secondary mailbox that appears in Outlook alongside the primary mailbox, with automatic or manual moves based on retention policies, and retrieval on demand without user intervention.
What is In-Place Archive?
In-Place Archive (also called the archive mailbox) is a secondary mailbox in Exchange Online that provides additional storage for a user's email. It is not a separate mailbox database; rather, it is a logical container within the same Exchange Online infrastructure. The archive mailbox appears in Outlook (desktop, web, and mobile) as a separate folder tree, typically named 'Online Archive - <user>'. Users can drag items between their primary mailbox and archive, or they can rely on retention policies to automatically move items after a specified period.
Why Does In-Place Archive Exist?
The primary driver is mailbox size management. Exchange Online primary mailboxes have a default storage limit of 50 GB for most subscription plans (except Exchange Online Plan 1 and Microsoft 365 Business Basic, which have 50 GB as well; Plan 2 and Enterprise E3/E5 have 100 GB). When users reach these limits, they cannot send or receive email. Archives provide a cost-effective way to offload older or less frequently accessed items without requiring manual deletion or pst files. Additionally, archives support compliance requirements by allowing organizations to retain email for long periods without overwhelming the primary mailbox.
How In-Place Archive Works Internally
When an archive is enabled for a user, Exchange Online creates a second mailbox object linked to the user's primary mailbox. The archive has its own set of folders (Inbox, Sent Items, Deleted Items, etc.) but shares the same user identity. From a backend perspective, both mailboxes are stored in the same mailbox database but are treated as separate items in the information store.
When a retention policy moves an item from primary to archive, the system performs a 'move' operation: the item is copied to the archive mailbox, and the original item in the primary mailbox is deleted. The move is not a simple tag or pointer; the item physically resides in the archive mailbox. However, to the user, the item appears in the same folder location under the archive folder tree. The user can still search across both mailboxes using Outlook's search capabilities.
Key Components, Values, Defaults, and Timers
Default storage limits: Primary mailbox: 50 GB (most subscriptions), 100 GB (E3/E5, Plan 2). Archive mailbox: 50 GB default, but can be expanded to 1.5 TB (auto-expanding archiving).
Auto-expanding archiving: Enabled by default for all users with an archive mailbox. When the archive reaches 90% of its current quota (e.g., 45 GB of 50 GB), Exchange Online automatically adds additional storage in increments of 100 GB, up to 1.5 TB. This process is transparent to the user.
Retention policies: Managed via the Microsoft 365 compliance center or Exchange admin center. A retention policy can be applied to a user or a group of users. The policy contains retention tags that define actions (move to archive, delete, or mark as expired) after a specified period (e.g., 30 days, 1 year, 5 years).
Default retention policy: Exchange Online has a default MRM policy (Default MRM Policy) that includes tags like '1 month move to archive', '1 year move to archive', and 'Never delete'. These are applied to all mailboxes unless a custom policy is assigned.
Litigation hold: When a mailbox is placed on litigation hold, the archive is also placed on hold. Items in the archive cannot be permanently deleted until the hold is removed.
Configuration and Verification Commands
To enable an archive via PowerShell:
Enable-Mailbox -Identity user@contoso.com -ArchiveTo verify archive status:
Get-Mailbox -Identity user@contoso.com | fl DisplayName,ArchiveStatus,ArchiveDatabase,ArchiveQuotaTo create a retention policy with a tag that moves items after 30 days:
New-RetentionPolicyTag -Name "30 days to archive" -Type All -AgeLimitForRetention 30 -RetentionAction MoveToArchive
New-RetentionPolicy -Name "Custom Archive Policy" -RetentionPolicyTagLinks "30 days to archive"
Set-Mailbox -Identity user@contoso.com -RetentionPolicy "Custom Archive Policy"How In-Place Archive Interacts with Related Technologies
eDiscovery: When performing an eDiscovery search, both primary and archive mailboxes are searched by default. You must explicitly exclude archive mailboxes if you only want primary.
Litigation Hold: Places a hold on both primary and archive mailboxes. Items in the archive are protected from deletion.
Retention Policies vs. Archive Policies: Retention policies can delete or retain items, but archive policies specifically move items to the archive. The exam tests the distinction: archive is a storage location, retention is a time-based action.
Mailbox Size Limits: If a user's primary mailbox exceeds its quota, they cannot send or receive mail. Archiving helps prevent this, but the archive itself also has quotas (default 50 GB, expandable to 1.5 TB).
Common Misunderstandings
Archive is not backup: Archiving moves items from primary to archive; it does not create a copy. If an item is deleted from the archive, it is gone (unless a hold is in place).
Archive does not reduce primary mailbox size automatically: You must apply retention policies to move items. Manual drag-and-drop also works but is not automatic.
Archive storage is not unlimited: While auto-expanding can reach 1.5 TB, there is a cap. For very large archives, consider third-party archiving solutions.
Archive is not available in all plans: Exchange Online Plan 1 includes a 50 GB archive; Plan 2 includes a 100 GB primary and 50 GB archive. Some Microsoft 365 Business plans also include archive.
Exam-First Details
MS-900 tests the concept of In-Place Archive as a compliance feature, not just storage. Questions often ask: 'Which feature allows users to store older email while still being able to access it?' Answer: In-Place Archive.
Know the default archive size: 50 GB.
Know that auto-expanding archiving is on by default and can increase archive to 1.5 TB.
Understand that retention policies can be used to automatically move items to the archive.
Be aware that litigation hold preserves both primary and archive mailboxes.
Trap: Some candidates confuse archive with backup. Archive moves items; backup copies them. Archive is for storage management; backup is for disaster recovery.
Another trap: Thinking archive automatically deletes items. It does not; it only moves items. Deletion requires a separate retention policy tag with 'Delete' action.
The exam may ask: 'What happens if a user exceeds the archive quota?' Answer: The user can still access the archive but cannot move new items to it until space is freed.
Step-by-Step: How a Retention Policy Moves an Item to Archive
Policy Application: An admin assigns a retention policy to a user's mailbox. The policy contains a tag with 'MoveToArchive' action and an age limit (e.g., 30 days).
Item Aging: The Managed Folder Assistant (MFA) runs periodically (every 7 days by default) and evaluates items in the user's primary mailbox. It checks the age of each item based on the date received or created.
Qualification: If an item is older than the age limit specified in the retention tag (e.g., 30 days), it qualifies for the action. The MFA identifies that the action is 'MoveToArchive'.
Move Operation: The MFA copies the item from the primary mailbox to the archive mailbox. The item is added to the corresponding folder in the archive (e.g., Inbox in primary becomes Inbox in archive).
Deletion from Primary: After the copy is confirmed successful, the MFA deletes the original item from the primary mailbox. The item now resides only in the archive.
User Experience: The user sees the item disappear from the primary mailbox folder and appear in the archive folder. In Outlook, the archive folder is listed under 'Online Archive - <user>'. The user can open the item normally.
Troubleshooting Common Issues
MFA not running: If items are not moving, check that the MFA is enabled and the mailbox has an applied retention policy. Use Get-MailboxFolderStatistics to see item counts.
Archive quota reached: If the archive is full, moves fail. Check archive quota with Get-Mailbox -Identity user | fl ArchiveQuota,ArchiveWarningQuota,ArchiveStatus.
Policy not applied: Verify that the retention policy is correctly assigned and that the tags are enabled.
Real-World Deployment Scenarios
Scenario 1: Large Enterprise Compliance A financial firm must retain all email for 7 years. They enable In-Place Archive for all employees and apply a retention policy that moves items older than 1 year to the archive. The archive auto-expands as needed. This keeps the primary mailbox under 50 GB and ensures compliance. They also place litigation hold on all mailboxes to prevent deletion.
Scenario 2: SMB Storage Management A small business uses Microsoft 365 Business Basic (50 GB primary). Employees frequently hit the limit. The admin enables archive and creates a policy to move items older than 6 months. This reduces support tickets and avoids the need for pst files.
Scenario 3: Legal Hold with Archive A legal team requires preservation of all email for a case. They place litigation hold on the relevant mailboxes. The archive is automatically included. Even if an admin tries to delete items from the archive, they are preserved in the recoverable items folder.
Performance Considerations
Archive retrieval is slightly slower than primary mailbox access because items are stored in a different logical container. However, for most users, the difference is negligible.
Auto-expanding archiving adds storage in 100 GB increments. This process is transparent but may take a few hours to complete.
Large archives (over 100 GB) may cause Outlook to take longer to sync folder hierarchy. Consider using Outlook in Online Mode or Outlook on the web for better performance.
Common Misconfigurations
Not enabling auto-expanding: By default, auto-expanding is on, but if an admin disables it, the archive is limited to 50 GB. Users will hit the limit quickly.
Forgetting to apply policies: Enabling archive without retention policies means users must manually move items. Many users forget, and their primary mailbox still fills up.
Confusing archive with backup: Some admins think archive provides disaster recovery. It does not; if a mailbox is deleted, the archive is also deleted. Use backup or retention policies with deletion protection.
Integration with Microsoft 365 Compliance Center
In the Microsoft 365 compliance center, archiving is managed under 'Data lifecycle management' > 'Exchange (legacy)'. Here you can create retention tags and policies. The compliance center also shows the status of archives and allows you to enable/disable archiving for users.
Exam-Specific Numbers
Default primary mailbox size: 50 GB (most plans), 100 GB (E3/E5, Plan 2)
Default archive mailbox size: 50 GB
Auto-expanding archive maximum: 1.5 TB
Auto-expanding trigger: when archive reaches 90% of its quota
Retention policy default run interval: 7 days (Managed Folder Assistant)
Age limits: commonly 30 days, 1 year, 5 years, etc.
Exam Traps
Trap: Archive is the same as backup. Reality: Archive moves items; backup copies them. Archive does not protect against accidental deletion unless a hold is applied.
Trap: Archive automatically deletes old items. Reality: Archive moves items; deletion requires a separate retention tag with 'Delete' action.
Trap: Archive is unlimited. Reality: Archive has a maximum of 1.5 TB with auto-expanding. It is not truly unlimited.
Trap: Archive is only for email. Reality: Archive can also hold calendar items, contacts, and tasks, though typically only email is archived.
Trap: Litigation hold only applies to primary mailbox. Reality: Litigation hold applies to both primary and archive mailboxes.
Comparison: In-Place Archive vs. PST Files
| Feature | In-Place Archive | PST Files | |---------|-----------------|-----------| | Accessibility | Accessible from Outlook, OWA, mobile | Only from the specific device where PST is stored | | Searchability | Searchable across both mailboxes | Not searchable from server; must be opened locally | | Management | Centralized via admin policies | User-managed; no compliance control | | Security | Encrypted at rest and in transit | Unencrypted; prone to loss | | Cost | Included in subscription | Free but requires manual backup |
Key Takeaways
In-Place Archive provides additional storage for email in Exchange Online, appearing as a separate mailbox in Outlook.
Default archive size is 50 GB, but auto-expanding can increase it to 1.5 TB.
Archive is not backup; it moves items from primary to archive, not copies them.
Retention policies automate the move of items to the archive based on age.
Litigation hold preserves both primary and archive mailboxes.
The Managed Folder Assistant runs every 7 days to process retention policies.
Auto-expanding triggers at 90% of the current archive quota.
Archive is a compliance feature, not just a storage optimization.
Wrong answers on the exam often confuse archive with backup or deletion.
Know the default quotas and the auto-expanding mechanism.
Use PowerShell commands like Enable-Mailbox -Archive to enable archiving.
Frequently Asked Questions
Q: Does In-Place Archive count against the user's primary mailbox quota? A: No. The archive has its own quota (default 50 GB). The primary mailbox and archive are separate.
Q: Can I access the archive on a mobile device? A: Yes, using the Outlook mobile app. The archive appears as a separate folder.
Q: What happens if I delete an item from the archive? A: The item is moved to the Deleted Items folder in the archive. If you empty that folder, the item is permanently deleted unless a hold is in place.
Q: Can I disable archiving for a user? A: Yes. You can disable the archive mailbox, but any items in the archive are moved back to the primary mailbox only if you use a retention policy; otherwise, they may be lost.
Q: Does archiving affect eDiscovery searches? A: Yes. By default, eDiscovery searches include both primary and archive mailboxes. You can exclude archives if needed.
Q: Is In-Place Archive available in all Microsoft 365 plans? A: No. It is available in Exchange Online Plan 1 and 2, and most Microsoft 365 Business and Enterprise plans. Check your specific plan.
Q: How do I enable auto-expanding archiving? A: It is enabled by default for all users with an archive. No action needed.
Q: Can I set a custom archive quota?
A: Yes, using PowerShell. For example: Set-Mailbox -Identity user -ArchiveQuota 100GB -ArchiveWarningQuota 90GB.
Quiz Questions
1. What is the default storage limit for an In-Place Archive mailbox in Exchange Online? A. 50 GB B. 100 GB C. 1.5 TB D. Unlimited Answer: A. The default archive mailbox size is 50 GB. Auto-expanding can increase it to 1.5 TB, but the default is 50 GB.
2. Which of the following best describes the purpose of In-Place Archive? A. To back up email data for disaster recovery B. To provide additional storage for older email items while keeping them accessible C. To automatically delete email older than a specified period D. To encrypt email at rest Answer: B. In-Place Archive moves older items to a secondary mailbox for storage management, not backup or deletion.
3. What triggers the auto-expanding feature in an archive mailbox? A. When the archive reaches 50% of its quota B. When the archive reaches 75% of its quota C. When the archive reaches 90% of its quota D. When the archive reaches 100% of its quota Answer: C. Auto-expanding triggers when the archive is 90% full.
4. A user is placed on litigation hold. Which mailboxes are affected? A. Only the primary mailbox B. Only the archive mailbox C. Both primary and archive mailboxes D. Neither mailbox Answer: C. Litigation hold applies to both primary and archive mailboxes.
5. How often does the Managed Folder Assistant run to process retention policies? A. Every day B. Every 7 days C. Every 30 days D. Every hour Answer: B. The MFA runs every 7 days by default.
Enable Archive Mailbox for User
An admin enables the archive mailbox for a user via Exchange admin center or PowerShell. This creates a secondary mailbox object linked to the user. The archive appears in Outlook automatically within a few minutes. The user sees an additional folder tree named 'Online Archive - <user>'. No data is moved at this point.
Assign Retention Policy
The admin assigns a retention policy to the user's mailbox. The policy contains retention tags that specify actions (move to archive, delete) after a certain age. For example, a tag might move items older than 30 days to the archive. The policy can be assigned to individual users or groups.
Managed Folder Assistant Runs
The Managed Folder Assistant (MFA) runs automatically every 7 days in Exchange Online. It processes mailboxes that have retention policies applied. It evaluates each item's age against the retention tags. Items that meet the age criteria are flagged for the specified action.
Item Move to Archive Executed
For items flagged with 'MoveToArchive', the MFA copies the item from the primary mailbox to the corresponding folder in the archive mailbox. After the copy is verified, the original item is deleted from the primary mailbox. The item now resides only in the archive. The user sees the item in the archive folder.
Auto-Expanding Trigger (if needed)
If the archive mailbox reaches 90% of its current quota (e.g., 45 GB of 50 GB), Exchange Online automatically adds additional storage in 100 GB increments. This process is transparent. The user can continue to move items to the archive. The maximum total archive size is 1.5 TB.
In a large enterprise with 10,000 users, the default primary mailbox size of 50 GB is quickly consumed by email-heavy departments like sales and legal. The company enables In-Place Archive for all users and creates a custom retention policy that moves items older than 1 year to the archive. This policy is applied to all mailboxes via a group policy. The archive auto-expands as needed. The IT team monitors archive usage monthly. They notice that some users have archives nearing 1.5 TB. For these users, they consider implementing a third-party archiving solution or increasing the archive quota beyond 1.5 TB (not possible natively). The company also enables litigation hold on all mailboxes to ensure compliance with regulatory requirements. A common issue they encounter is that the Managed Folder Assistant sometimes lags behind, causing primary mailboxes to fill up before items are moved. They mitigate this by running the MFA manually via PowerShell: Start-ManagedFolderAssistant -Identity user@contoso.com.
In a mid-sized law firm, attorneys need to retain email for 7 years. The firm enables In-Place Archive and creates a retention policy with multiple tags: move items older than 6 months to archive, delete items after 7 years. They also place litigation hold on all mailboxes. The archive size grows slowly. After 5 years, some archives reach 100 GB. The firm uses eDiscovery to search across both primary and archive mailboxes for case preparation. A problem they face is that some attorneys manually delete emails from the archive, thinking it frees up space. In reality, deleted items go to the Deleted Items folder in the archive and still count against the quota until emptied. The IT team trains users to use retention policies instead of manual deletion.
In a small business with 50 users, the admin enables archive for all users but does not apply any retention policy. Users are told to manually drag items to the archive. After a few months, the primary mailboxes are still full because users forget to archive. The admin then creates a policy to automatically move items older than 6 months. This solves the problem. The admin also learns that archive storage is included in their Microsoft 365 Business Basic subscription, so no extra cost. They monitor archive sizes and find that auto-expanding works well, with some users reaching 200 GB without issues.
The MS-900 exam tests In-Place Archive under objective 3.4: 'Describe the compliance management capabilities in Microsoft 365.' Specifically, you should know:
That In-Place Archive is a feature of Exchange Online that provides additional mailbox storage.
The default archive size is 50 GB, but auto-expanding can increase it to 1.5 TB.
Archive is not backup; it moves items, not copies.
Retention policies can automate moving items to the archive.
Litigation hold applies to both primary and archive mailboxes.
The Managed Folder Assistant runs every 7 days.
Common wrong answers on exam questions: 1. 'Archive automatically deletes old emails.' Reality: Archive moves emails; deletion requires a separate 'Delete' action. 2. 'Archive is a backup solution.' Reality: Archive does not create copies; if you delete from archive, it's gone (unless on hold). 3. 'Archive has unlimited storage.' Reality: Maximum 1.5 TB with auto-expanding. 4. 'Archive is only available in Enterprise plans.' Reality: Available in many plans including Business Basic. 5. 'Litigation hold only protects primary mailbox.' Reality: Protects both.
Numbers that appear verbatim on the exam: - 50 GB default archive quota - 1.5 TB maximum with auto-expanding - 90% threshold for auto-expanding trigger - 7 days for Managed Folder Assistant run interval
Edge cases the exam loves:
What happens if archive quota is reached? Answer: Items cannot be moved to archive until space is freed.
Can you access archive from Outlook mobile? Answer: Yes.
Does archive count against the 50 GB primary quota? Answer: No.
How to eliminate wrong answers:
If the answer mentions 'backup' or 'copy', it's likely wrong.
If the answer says 'unlimited', it's wrong (1.5 TB max).
If the answer says 'automatic deletion', it's wrong unless the question specifies a 'Delete' retention tag.
If the answer says 'only primary mailbox' for litigation hold, it's wrong.
Remember: Archive is a compliance feature for storage management, not data protection. It works hand-in-hand with retention policies and litigation hold.
In-Place Archive provides a secondary mailbox for additional email storage, default size 50 GB, auto-expanding to 1.5 TB.
Archive is not backup; it moves items from primary to archive, not copies them.
Retention policies automate moving items to the archive based on age (e.g., 30 days, 1 year).
Litigation hold preserves both primary and archive mailboxes.
The Managed Folder Assistant runs every 7 days to process retention policies.
Auto-expanding triggers when the archive reaches 90% of its current quota.
Archive storage is separate from primary mailbox quota.
Wrong exam answers often confuse archive with backup or deletion.
Archive is available in Exchange Online Plan 1 and 2, and most Microsoft 365 Business and Enterprise plans.
Use PowerShell commands like Enable-Mailbox -Archive to enable archiving.
These come up on the exam all the time. Here's how to tell them apart.
In-Place Archive
Centralized management via admin policies
Accessible from Outlook, OWA, and mobile devices
Searchable across both primary and archive mailboxes
Encrypted at rest and in transit
Included in Exchange Online subscription
PST Files
User-managed; no central control
Only accessible from the device where PST is stored
Not searchable from server; must be opened locally
Unencrypted; prone to loss or theft
Requires manual backup; no built-in compliance features
Mistake
In-Place Archive automatically deletes old emails from the primary mailbox.
Correct
Archive moves items to the secondary mailbox; it does not delete them. Deletion requires a separate retention policy tag with the 'Delete' action.
Mistake
In-Place Archive is a backup solution for email.
Correct
Archive moves items from primary to archive; it does not create a copy. If an item is deleted from the archive, it is permanently lost unless a hold is in place. Backup solutions like Exchange Online's native backup or third-party tools create copies for disaster recovery.
Mistake
In-Place Archive provides unlimited storage.
Correct
The archive has a default quota of 50 GB, which can auto-expand up to 1.5 TB. It is not unlimited. For larger storage needs, third-party archiving solutions may be required.
Mistake
Litigation hold only applies to the primary mailbox, not the archive.
Correct
Litigation hold applies to both primary and archive mailboxes. Items in the archive are preserved and cannot be permanently deleted until the hold is removed.
Mistake
Enabling In-Place Archive automatically reduces the primary mailbox size.
Correct
Enabling archive does not automatically move items. You must apply retention policies or manually move items to see a reduction in primary mailbox usage.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
The default archive mailbox size is 50 GB. However, auto-expanding archiving is enabled by default, which can increase the archive size up to 1.5 TB in 100 GB increments when the archive reaches 90% of its current quota.
No. The archive has its own quota (default 50 GB). The primary mailbox and archive are separate. Items moved to the archive free up space in the primary mailbox.
Yes, using the Outlook mobile app. The archive appears as a separate folder tree. Users can read and search archived emails from their mobile device.
The item is moved to the Deleted Items folder within the archive. If you empty that folder, the item is permanently deleted unless the mailbox is on litigation hold or has a retention policy that preserves the item.
No. It is available in Exchange Online Plan 1 and 2, and most Microsoft 365 Business and Enterprise plans (e.g., Business Basic, Business Standard, E3, E5). Check your specific plan's features.
Auto-expanding archiving is enabled by default for all users who have an archive mailbox. No additional configuration is needed. It automatically adds storage when the archive reaches 90% of its quota.
Yes, using PowerShell. For example: Set-Mailbox -Identity user -ArchiveQuota 100GB -ArchiveWarningQuota 90GB. This sets the maximum archive size to 100 GB and a warning at 90 GB.
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