When organisations plan email archiving projects, it’s common to focus on an incremental or “partial” migration. The idea sounds reasonable: start small, move user archives first, leave journals for later, or only migrate the most recent years of data. But what seems like a low-risk strategy often creates hidden operational, compliance and cost problems that end up costing more — both in time and risk — than a fully scoped migration.
Why partial migrations often fail
1. Data fragmentation becomes permanent
Partial migrations leave data split between the legacy archive and the new environment. Users don’t know where to look for old emails, Legal and Information Governance teams have to search multiple systems, and no one has a unified view. Instead of simplifying, partial migration perpetuates complexity, which undermines the whole point of moving to Microsoft 365 or Google Workspace.
2. Compliance blind spots increase
When only a subset of data is migrated, retention and deletion policies can’t be applied consistently. In the event of a FOI, SAR or litigation request, eDiscovery teams may need to run separate searches across both environments. Not only is this slower, but it’s also harder to defend under audit or regulatory scrutiny.
3. Hidden costs multiply
Legacy archive platforms are often priced on total data stored or mailboxes covered. Leaving old data behind means continuing to pay licensing and storage costs, even though you’ve invested in a new system. On top of that, IT teams may spend disproportionate time managing two systems, effectively doubling operational overhead.
4. Technical limitations undermine ROI
Partial migrations are often the result of perceived technical complexity — for example, concerns about extracting journals or very old PSTs. But when these challenges prevent a complete migration, they lock you into hybrid architectures that never truly deliver cloud benefits.
A better approach: comprehensive planning
A complete migration plan doesn’t have to happen overnight, but it should be scoped and executed as a single programme. This means:
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Full data discovery and classification
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Migration of both user and journal archives
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Policies designed with compliance and retention in mind
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Clear acceptance criteria and complete auditability
By moving everything at once, organisations eliminate friction, reduce long-term cost, and unlock the full benefits of modern cloud platforms.
Partial migrations might look easier at first.
But in the world of archive data, half-done usually means half-broken.
Want to scope out a full migration of your legacy data? Get in touch here: https://ultimatemigrator.com/contactus/