How do we migrate from IMAP or hosted email to Microsoft 365?

Key facts

• IMAP migration moves email folders only; calendars, contacts and tasks need another method.
• Mailboxes must exist and be licensed in Microsoft 365 before an IMAP migration batch runs.
• Third-party migration tools can move mail, calendars and contacts from many hosted platforms.
• MX, Autodiscover, SPF, DKIM and DMARC all need updating for the domain.
• The old host should stay active until the final incremental sync is done.

Know what you are migrating from

Hosted email covers a wide range: cPanel or web host mailboxes, ISP email, standalone IMAP services and hosted Exchange from a third-party provider. The source decides the method. IMAP-only services can be migrated with Microsoft's built-in IMAP migration. Hosted Exchange often supports cutover-style migrations or third-party tools that move calendars and contacts too.

Inventory mailboxes, sizes, aliases, shared accounts, distribution lists, forwarding rules and any devices or apps that send mail through the old server, such as scanners and line-of-business apps.

Choose the migration method

The right tool depends on what must move and how many users there are.

Step by step

A typical IMAP or hosted email migration follows the same pattern regardless of tool.

• Add and verify the domain in Microsoft 365, without changing MX yet.
• Create users, assign licenses, and add aliases and shared mailboxes.
• Lower the TTL on MX and Autodiscover records a few days ahead.
• Run the initial sync with IMAP migration batches or the third-party tool.
• Migrate calendars and contacts with the tool or by export and import.
• Switch MX to Exchange Online and update Autodiscover and SPF.
• Run a final incremental sync to catch mail that arrived on the old host.
• Set up Outlook and mobile devices, then enable DKIM and DMARC.

IMAP migration details to plan for

Exchange Online IMAP migration uses a CSV file listing each mailbox and its source sign-in details, or an administrator account if the source supports it. Treat that file as sensitive and delete it after migration. Large mailboxes and slow source servers can extend the initial sync, so start early and let it run in the background.

IMAP does not carry calendar items, contacts, rules or signatures. Users may need to recreate rules and signatures, which is worth a short guide. Folder names with unusual characters and very large items can fail; review migration reports and handle exceptions.

DNS, security and cleanup

Update MX to the Exchange Online endpoint, Autodiscover to Microsoft 365, and SPF to include Microsoft 365 while removing the old host once it no longer sends mail. Enable DKIM signing in Exchange Online and publish a DMARC policy, starting in monitoring mode. Moving off a basic hosted service is a good time to turn on MFA, Conditional Access and Defender for Office 365 protections.

Keep the old host active until the final sync and a few days of stable mail flow. Then cancel it, after exporting any mailboxes you need to keep for records.

How Accred Consulting approaches it

Accred Consulting migrates IMAP and hosted email as a scoped Exchange Online project. Discovery inventories mailboxes, sizes, aliases, calendars, shared accounts and apps that send mail, and the proposal sets scope, fixed price and timeline. The US-based specialists assigned to your engagement choose IMAP migration or a third-party tool based on what must move, set up users and DNS, run the syncs and cutover, and turn on MFA and email authentication. Handover includes documentation and knowledge transfer, with optional support retainers.

Track record: 475+ client projects, 2,000+ migration workstreams and 210,000+ users migrated by a US-based team. Company facts · Case studies

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