Overview
This guide outlines best practices for managing email retention and archiving in Microsoft 365. It is designed for IT support staff, system administrators, and service desk professionals responsible for Exchange Online mailboxes, compliance, and data lifecycle management.
Objectives
- Ensure compliance with legal and regulatory requirements
- Reduce data risk and unauthorized access
- Maintain mailbox accessibility for audits and investigations
- Standardize retention and archiving procedures
Retention Strategy
1. Define Retention Requirements
Before applying technical controls, organizations should identify and document:
- Legal and regulatory email retention obligations
- Internal audit and record-keeping requirements
- Business needs for historical communication access
Retention requirements must be approved by IT, legal, and compliance stakeholders.
2. Use Retention Policies as the Primary Control
Microsoft Purview retention policies should be the main mechanism for managing email data.
Best Practices:
- Apply retention policies consistently across all mailboxes
- Avoid reliance on end-user mailbox management
- Review and update retention configurations regularly
Manual mailbox exports should only be used when retention policies cannot meet specific compliance needs.
Archiving Mailboxes
Recommended Archiving Methods
Preferred approaches include:
- Exchange Online Archiving for long-term retention
- Shared mailboxes for inactive or departed users
- Keep data within Microsoft 365 to preserve search and audit capabilities
Avoid: Unmanaged PST files stored locally whenever possible.
Mailbox Exports (Compliance Use Cases)
When Mailbox Exports Are Required
Exports may be necessary for:
- Legal discovery requests
- Regulatory or internal audits
- Employee offboarding
- Data preservation for investigations
Microsoft 365 supports mailbox exports through Microsoft Purview eDiscovery tools.
Internal Reference Guide
For detailed export procedures, permissions, and security considerations, refer to:
Exporting an Office 365 Mailbox to PST
This guide covers:
- Required administrative roles
- Content Search configuration
- Secure PST export and download process
Securing Archived and Exported Data
When handling archived or exported mailbox data:
- Encrypt data at rest and in transit
- Restrict access using role-based controls
- Store data in approved, secure locations
- Retain exported data only as long as necessary
- Log and document all export actions
Related Documentation
- Exporting an Office 365 Mailbox to PST (Internal)(Download PDF)
- Microsoft Purview – Retention Policies
- Exchange Online Archiving
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