How to Successfully Migrate Legacy Data

As we move further into 2025, organizations are confronting a wave of modernization challenges. One of the most complex issues is what to do with decades of accumulated legacy data. Whether it lives in aging archives, home drives, PST files, or older email systems, this data often carries business, legal, and compliance value. But migrating it into a modern cloud environment like Microsoft 365 requires more than simply copying files from one place to another. 

This refreshed guide looks at legacy data migrations through a modern lens, focusing on modern risks, new technology considerations, and practical strategies that matter today, without product pitches or platform promotion. 

Key Takeaways for 2025 

• Legacy data now includes far more than PST files; organizations must account for email archives, personal storage, shared drives, collaboration platforms, and fragmented cloud repositories. 
• Migration is no longer just a technical task; it requires user experience planning, legal defensibility, communication workflows, and clean-up strategies. 
• AI-powered classification, compliance automation, and retention modernization are now central to handling legacy data. 
• “Successful migration” in 2025 focuses on completeness, defensibility, transparency, and post-migration usability, not just data transfer. 

What Counts as Legacy Data in 2025? 

Legacy Data still includes well-known data types like PSTs, large home drive folders, and email archives, but the landscape has expanded. Today, organizations may be dealing with:

• Decades-old email archives from systems like Enterprise Vault or EMC SourceOne 
• Home drives and file shares with mixed active and inactive data 
• Dormant collaboration spaces (Teams, Slack, SharePoint sites) tied to departed employees 
• “Dark data” that has no ownership, tagging, or clear purpose 
• Personal storage artifacts accumulated before proper governance policies existed 

Because many repositories now include a blend of active and inactive data, migration requires a strategy that preserves accessibility without bringing unnecessary clutter into the cloud. 

What Does Legacy Data Migration Mean Today? 

In 2025, organizations have three primary options: 

1. Migrate the Data

Move the full repository into Microsoft 365 or another cloud environment. 

2. Modernize and Reduce

Use retention policies, classification, or defensible disposition to remove redundant or low-value data before migrating. 

3. Leave the System Behind and Extract Only What Matters

Some organizations now choose to migrate only the data with business, regulatory, or litigation value. 

For those choosing migration, typical target destinations still include: 

• PST → Microsoft 365 archive mailbox 
• Corporate email → Primary mailbox 
• File shares/home drives → OneDrive or SharePoint 
• Email archives → Microsoft 365 archive or mailbox 

But unlike years past, migrations now often involve decision-making around retention labels, sensitivity labels, immutable storage, and searchability. 

Is Data Migration Still Hard? (Short answer: Yes, but differently) 

Legacy data migration can still be performed manually, but the complexity of today’s environments makes manual processes increasingly risky. 

The challenges that organizations face in 2025 include: 

• Sheer data volume, often spanning multiple generations of systems 
• Legal and regulatory pressure, especially for financial services, healthcare, and global enterprises 
• User impact, particularly for employees who still rely on older archives for historical content 
• Error-prone source systems, where corruption or partial metadata is common 
• Cloud governance requirements, which now require more structured, policy-aligned data than ever 

Modern approaches rely heavily on automation, orchestration, and reporting, not just file copying, to keep projects predictable and defensible. 

What Does “Success” Look Like in 2025 for Legacy Data Migrations? 

Organizations are defining successful legacy data migration through broader criteria than a decade ago. A migration is considered successful when: 

• Users experience minimal disruption, and know where their data went 
• Data is searchable, accessible, and properly categorized after migration 
• Compliance and legal teams have clear reporting on what moved, what didn’t, and why 
• Errors and exceptions are tracked and remediated, not ignored 
• Source systems can be fully decommissioned, reducing cost and risk 
• The organization avoids bringing low-value or risky data into its cloud tenant 

Success today is holistic, covering people, process, technology, and governance. 

Why Organizations Still Need Help with Legacy Data 

Even with modern tools, legacy data migration remains one of the most complex operational challenges in IT. The reasons include: 

• Every organization has unique repositories, history, and retention needs. 
• Legacy systems often behave unpredictably after years of storage growth or neglect. 
• Data ownership is unclear for many older archives. 
• Legal and regulatory expectations continue to tighten. 

Most enterprises now look for experienced partners not just to move data, but to guide the decision-making around: 

Migration vs. defensible disposition: Organizations must now decide not only how to migrate data, but whether the data should be migrated at all. This involves assessing business value, regulatory obligations, litigation risk, and user needs. Defensible disposition offers the opportunity to remove redundant, obsolete, or low-value information in a way that is legally justifiable and fully documented, reducing both cost and risk before moving anything into the cloud. 

Mapping data into modern governance frameworks. Legacy systems often predate today’s retention labels, sensitivity classifications, and regulatory requirements. Before migration, organizations must determine how older content aligns with modern governance structures. Ensuring the data is correctly labeled, retained, protected, and discoverable once it arrives in Microsoft 365 or any modern cloud environment. This step helps prevent compliance gaps and improves long-term search and management. 

Ensuring user communication and change management, migrating historical data can affect end users more than expected. Employees may lose access to legacy systems, see changes in folder structure, or need guidance on where specific content has been relocated. Clear, timely communication and change management planning are essential for minimizing disruption, increasing adoption, and preventing support tickets during and after the migration. 

Validating completeness and chain of custody. Modern migrations place greater emphasis on transparency and defensibility. Organizations must be able to prove that data was collected, processed, transferred, and stored with full integrity. This includes validating message counts, metadata preservation, exceptions reporting, and maintaining a reliable chain of custody from extraction to final storage. These verification steps ensure compliance, reduce legal exposure, and support eventual system decommissioning. 

Preparing for Your 2025 Data Migration Project 

To help organizations plan effectively, here is a quick overview of the 7 essential steps for a successful data migration, summarized in a very short form: 

• Assess – Understand your current data, systems, and risks. 
• Strategize – Decide what moves, what stays, and what can be defensibly deleted. 
• Prepare – Clean, classify, and organize data before migration. 
• Plan – Establish timelines, workflows, and communication plans. 
• Migrate – Execute the data transfer securely and efficiently. 
• Validate – Verify accuracy, completeness, and chain of custody. 
• Decommission – Retire legacy systems and finalize governance. 

These steps provide the foundation for a predictable, defensible, and successful migration. 

Cloudficient specializes in cloud migration services, including onboarding for Microsoft 365, Enterprise Vault migration, compliance migrations, and more. With our help, you can be confident that your data migration process will be completed on budget, on time, and according to your requirements. 

With unmatched next-generation migration technology, Cloudficient is revolutionizing the way businesses retire legacy systems and transform their organization into the cloud. Our business constantly remains focused on client needs and creating product offerings that match them.