Six weeks after a mid-sized accounting practice moved from an on-premise Exchange server to Microsoft 365, a client's solicitor sent a request for all correspondence relating to a 2022 tax dispute. The practice manager searched the new mailboxes, then the archive folders, then asked IT to check the old server. The old server had been decommissioned as part of the migration. The migration vendor had moved active mailboxes and calendars. Nobody had been asked to move — or even preserve — the archive. Three years of correspondence existed only in a backup tape nobody was confident they could restore.
This happens more often than it should, and it's rarely because anyone was careless. It's because email migration projects are scoped around getting people working on the new platform, not around preserving the historical record. Archiving is treated as something the new platform will "just handle," when in most cases it won't — not in the way a regulator or a court expects.
What the compliance requirement actually is
If you're a law firm, accounting practice, or financial advisory business, your retention obligations don't pause during a system migration — and they don't reset either. In NSW, the Legal Profession Uniform Law and associated conduct rules require client files to be retained for at least 7 years after a matter closes; other Australian states have equivalent rules under the Legal Profession Uniform Law framework. Financial advisers face record-keeping obligations under the Corporations Act 2001 (s912E and related ASIC guidance) and, where AML/CTF obligations apply, under the AML/CTF Act 2006, which generally requires 7 years of transaction and customer records. In the UK, SRA Standards and Regulations require firms to keep client files accessible for the relevant limitation period, and FCA-regulated advisers fall under SYSC 9, which requires records sufficient to enable the FCA to monitor compliance — typically 5 years, longer for pension transfer advice. None of these rules say "unless you changed email providers." A regulator or opposing counsel asking for correspondence from three years ago doesn't care that you moved from Google Workspace to Microsoft 365, or from an old on-premise server to a cloud host, in the meantime. The obligation to produce those records survives the migration, even if your archive didn't.
What most small firms actually do
Most migrations are planned by whoever's onboarding the new email platform — often an IT contractor optimising for uptime and mailbox continuity, not compliance continuity. The common approach is to sync active mailboxes, export a few PST files "just in case," and assume the old system stays accessible until someone remembers to switch it off. In practice, that old system gets decommissioned within months once licence costs bite, and the PST files end up on a shared drive, unindexed, unsearchable, and frequently corrupted or forgotten entirely. Sent mail is often the first casualty — teams focus on inbox migration and forget that sent items and BCC records need the same treatment. This works fine right up until someone needs to search five-year-old correspondence under time pressure, at which point it becomes very clear that "it's in a PST somewhere" is not a retrieval process.
What good looks like
An audit-ready archive survives a provider migration because it was never dependent on the mail provider in the first place. The archive sits as an independent layer that captures every message — sent and received — continuously, at the point it's sent or delivered, rather than being reconstructed from whatever happens to still be in a mailbox when someone remembers to check. That means the archive doesn't need to be "migrated" at all when you change providers; it just keeps capturing from the new platform the same way it captured from the old one.
A few characteristics matter in practice. The archive should be tamper-evident — records can't be quietly altered or deleted after capture, which matters if you're ever asked to demonstrate chain of custody. It should preserve full metadata: headers, timestamps, recipients, attachments, not just message bodies. It needs to be searchable and retrievable quickly, not just stored — a regulator's request typically comes with a deadline measured in days, not months. And critically, it needs to cover sent mail and internal correspondence, not just what lands in an inbox, because "all correspondence" is what most retention rules actually require.
Tools like AutoArchive Mail are built around this separation deliberately: the archive connects to your mail platform via a standard protocol, captures continuously in the background, and keeps operating independently of whichever provider you're using this year. When a migration happens, the archive isn't part of what has to move — it just keeps running.
The practical path forward
If a provider switch is on the horizon, sequence it properly. First, confirm what's actually being archived today — check whether your current setup captures sent mail and attachments, not just inbox content, and export a sample to verify it's genuinely retrievable. Second, set up independent archiving before the migration starts, not after, so there's no gap in continuous capture during cutover. Third, keep the old platform in read-only mode until you've confirmed the new archive is capturing correctly and a spot-check retrieval from the old system succeeds — don't decommission on the vendor's default timeline. You can get independent archiving running in under 30 minutes; if you want to test this before committing to a migration date, you can Start Free Trial and have capture running alongside your current setup well before the switch happens. Fourth, if you're a regulated firm with more than a few years of retained correspondence or an active matter involving litigation holds, get your compliance adviser or IT provider involved in the migration plan specifically — not just the mailbox cutover.
One thing this doesn't cover
This guide addresses keeping your historical email record intact through a provider switch — it doesn't cover migrating active mailbox content, calendars, or contacts, which is a separate technical project with its own tooling and risks. If you're mid-migration and unsure whether historical data has already been lost, that's a question for a forensic IT specialist, not a blog post.
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