Cloud2Cloud Migrator extracts historical email from your Mimecast archive and lands it in Microsoft 365 with timestamps, recipients, headers, attachments and folder structure preserved. Every message is accounted for in an exportable audit trail.
Many organisations adopted Mimecast's cloud archive when Exchange was on-premises and Microsoft's native archiving was limited. Now that mail lives in Microsoft 365, keeping years of history in a separate archive means paying twice, searching in two places, and running eDiscovery and retention across two systems.
Bringing that history into Microsoft 365 puts it under one set of Purview retention policies, one eDiscovery workflow and one search experience for users. The challenge is getting it out completely and provably, without breaking the audit trail your regulators rely on.
Archive migrations often break mid-flight, and when they restart they copy everything again, filling Microsoft 365 with duplicates. We checkpoint every message, so a migration that fails at 87% resumes at 87%, not zero.
Mimecast retention and Microsoft 365 retention don't map one-to-one. Before any data moves, we profile what's in the archive and work with your records and compliance teams to decide where each class of data should land: the user's mailbox, an online archive, or a compliance hold under a specific retention label. That decision is far cheaper to make before migration than after.
Our engine has been used by financial services firms, healthcare organisations and government bodies, where an incomplete archive migration is a regulatory finding. Agents can run in your own infrastructure and in-region, role-based access lets regional teams run their own waves, and the audit trail exports as signed CSV, JSON or PDF.
Sanderson Weatherall left its Mimecast archive for less than half the provider's quoted extraction fee of $5,000 per terabyte, and finished inside a 16-week deadline to avoid a renewal. Read the case study → A US healthcare provider used the same approach to move a Proofpoint journal archive into Microsoft 365.
Many Mimecast exits are part of a wider consolidation alongside PST estates, Enterprise Vault or tenant-to-tenant moves after a merger. One engine, one console and one audit trail cover all of them. See PST migration and Enterprise Vault migration.
Work backwards from the date your Mimecast archive subscription ends. Extracting many years of history takes time, and you need read access to the archive until the final wave has been reconciled and signed off. Starting too late is the most common reason Mimecast exits end up rushed or need an expensive short-term renewal.
We profile what's in the archive: volume per user, date ranges and leavers. Leavers matter more than people expect. Mimecast often holds years of mail for people whose Microsoft 365 mailboxes were deleted long ago, so that content needs a destination, typically a dedicated mailbox under a retention hold, rather than being dropped.
Mimecast archives usually capture mail as it's sent and received, so the archive contains copies of many messages that are still in users' mailboxes. It also contains messages users deliberately deleted. Pouring everything into users' primary mailboxes would duplicate the first group and resurface the second. Landing archive content in the online archive or a compliance destination avoids both problems. We agree the approach with your records team before migration starts.
Mimecast retention settings and Microsoft Purview retention labels and policies need to be mapped explicitly, as described above. Any content under legal hold must remain held throughout.
A pilot wave establishes real throughput and validates the reconciliation output. Production waves then run by department or region, scheduled around working hours, with distributed agents working on many mailboxes in parallel.
Each wave produces a per-message reconciliation report. Once Legal and compliance sign off the final wave, the archive subscription can end. Keep the exported audit trail as the record that the archive was moved in full.
Retiring the Mimecast archive doesn't mean retiring Mimecast. Many organisations keep its email security gateway and only move the archive, because consolidating archive and compliance into Microsoft 365 is a separate decision from how inbound mail is filtered. Migration works the same either way.
At the end of a Mimecast exit, Legal and compliance usually ask three questions. Did everything come across? What didn't, and why? Can we prove it? The reconciliation report answers the first two: source and destination counts per mailbox, and every item that couldn't be migrated, listed with a reason. The signed audit trail answers the third. It records the source item, its destination, the timestamp, the agent and the result for every message, exportable as CSV, JSON or PDF. That is the evidence you need to close the project and end the subscription with confidence.
Starting too late. The extraction timeline is driven by volume and throttling, not by the contract end date. Leave too little time and you're negotiating a renewal under pressure.
Pouring everything into primary mailboxes. That duplicates mail users already have and resurfaces mail they deleted. It also inflates mailbox sizes and slows Outlook. The online archive or a compliance destination is usually the better landing place.
Forgetting leavers. The archive is often the only remaining copy of former employees' mail. If nobody plans a destination for it, it's lost when the subscription ends.
Letting holds lapse in transition. Content under legal hold in Mimecast must be under an equivalent Purview hold the moment it lands in Microsoft 365. Set up the holds before the data moves, not after.
Closing without evidence. "The vendor said it's done" won't satisfy an auditor or a regulator. Insist on per-message reconciliation and an exportable audit trail before you end the subscription.
Yes. We extract archived email from Mimecast and write it to Microsoft 365 mailboxes or online archives, preserving metadata and folder structure, with every message reconciled.
Yes. Timestamps, recipients, headers and attachments are retained, so the message in Microsoft 365 matches the original for search and eDiscovery.
Every message is checkpointed. The job resumes from the last successful item with no duplicates and no re-scan.
Every action is logged with source, destination, timestamp, agent and result, and counts are reconciled between source and destination. Items that couldn't migrate are listed with the reason. The report exports as CSV, JSON or PDF.
Yes. Agents and the audit store can run on your own infrastructure in-region, so data moves straight from Mimecast to your Microsoft 365 tenant.
No. Migrating the archive is separate from how inbound mail is filtered. Many organisations keep the Mimecast gateway and only move the archive into Microsoft 365.
They need a destination before the Mimecast subscription ends. Typically that's a dedicated mailbox under a retention hold, so the content stays searchable for eDiscovery without recreating mailboxes for former staff.
Book a 30-minute scoping call with the engineers who built the engine. We'll map your sources, volumes and compliance constraints, and tell you honestly where we fit.
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