Email Migration Checklist: Everything You Need Before Switching

Migrating your business email to a new platform is one of the most consequential IT projects a UK business can undertake. Email is the communication backbone of virtually every organisation — it carries contracts, client correspondence, internal decisions, financial data, and compliance-sensitive information. A botched email migration can mean lost messages, days of disruption, broken client relationships, and even regulatory consequences under UK GDPR if personal data is compromised in the process.

Yet email migrations are performed routinely and successfully by thousands of UK businesses every year. The difference between a smooth migration and a disastrous one almost always comes down to preparation. Businesses that invest time in thorough planning, testing, and communication before the migration date experience minimal disruption. Those that rush the process inevitably encounter problems that could have been prevented.

This comprehensive checklist covers everything you need to plan, prepare, and execute a successful email migration, with a focus on the most common scenario for UK SMEs: migrating to Microsoft 365.

Phase 1: Pre-Migration Assessment

Before touching a single mailbox, you need to understand exactly what you are migrating, from where, to where, and why. This assessment phase is the foundation of a successful migration and should not be rushed.

Audit Your Current Email Environment

Document every aspect of your existing email system. How many mailboxes do you have? What are their sizes? Which email platform are you currently using — on-premises Exchange, hosted Exchange, Google Workspace, IMAP, or something else? Are there shared mailboxes, distribution lists, or aliases that need to be recreated? Do you have any email forwarding rules that must be preserved?

Identify all the ancillary services connected to your email. Calendar sharing, contacts, tasks, public folders, room booking systems, email signatures, disclaimers, transport rules, and archive solutions all need to be accounted for. Missing any of these during planning will cause problems during or after the migration.

Define Your Migration Scope

Decide exactly what data you are migrating. For most businesses, this includes emails, calendars, contacts, and tasks. However, you also need to decide how far back to migrate historical email. Migrating ten years of email for every user takes significantly longer and costs more than migrating the last two years. Consider archiving older data separately rather than migrating everything.

Migration Component	Complexity	Common Issues	Planning Required
User Mailboxes	Medium	Large mailboxes, corrupted items	Size audit, user communication
Shared Mailboxes	Medium	Permission mapping, access rights	Permission documentation
Distribution Lists	Low	Nested groups, external members	Membership verification
Calendars	Medium	Recurring events, shared calendars	Calendar sharing audit
Public Folders	High	Complex permissions, large data volumes	Migration tool selection, restructuring
Email Signatures	Low	Formatting differences between platforms	Template redesign for new platform
Transport Rules	Medium	Platform-specific syntax	Rule documentation and recreation

Phase 2: Technical Preparation

DNS and Domain Verification

Your email domain (the part after the @ symbol) is controlled by DNS records. Before migration, you need to verify domain ownership in Microsoft 365 by adding a TXT record to your domain's DNS. You should also identify your current MX records, SPF records, DKIM configuration, and DMARC policy — all of which will need to be updated during the migration.

It is critical to understand that changing MX records is the point of no return — once you redirect email delivery to Microsoft 365, the new system must be ready to receive it. Plan this DNS change carefully, ideally reducing the TTL (Time to Live) on your MX records to 300 seconds several days before migration so the switch propagates quickly.

Licencing and Account Setup

Ensure you have the correct Microsoft 365 licences for every user. For most UK SMEs, Microsoft 365 Business Premium provides the best combination of email, productivity tools, and security features. Create all user accounts in Microsoft 365 before migration begins, and assign the appropriate licences. Pre-creating accounts allows you to configure settings, test access, and resolve any issues before the migration window.

Phase 3: Migration Execution

Choose Your Migration Method

The migration method depends on your source platform. For on-premises Exchange, a hybrid migration or cutover migration is typical. For Google Workspace, Microsoft provides a dedicated migration tool. For IMAP-based systems, IMAP migration or a third-party tool like BitTitan MigrationWiz is commonly used.

Regardless of method, always perform a test migration first. Migrate a small number of pilot users — ideally technically confident staff who can identify and report issues — and verify that emails, calendars, and contacts have transferred correctly. Only proceed with the full migration once the pilot is successful.

The Migration Window

Schedule the migration during a period of low email activity — evenings, weekends, or bank holidays. Communicate the schedule to all staff well in advance, explaining what to expect, how long the disruption might last, and who to contact if they experience problems. Provide clear instructions for setting up email on their devices after migration.

Phase 4: Post-Migration Verification

After migration, verify that every mailbox has been transferred completely. Check that emails are being received at the new platform, that sent mail works correctly, that calendars and contacts are intact, and that shared mailboxes and distribution lists function as expected.

Update SPF, DKIM, and DMARC DNS records to authenticate email sent from Microsoft 365. Without these records, your outgoing email may be flagged as spam by recipients' email systems. SPF tells receiving servers which systems are authorised to send email on behalf of your domain. DKIM adds a cryptographic signature to your outgoing messages. DMARC ties SPF and DKIM together and tells receiving servers what to do with messages that fail authentication.

Monitor for bounced emails, delivery delays, and user-reported issues for at least two weeks after migration. Some problems — such as emails from specific senders being rejected, or calendar sync issues with particular devices — may only surface over time as different scenarios are encountered.

Security Considerations

An email migration is an opportunity to improve your security posture. Configure Microsoft 365 security features from day one: enable multi-factor authentication for all users, configure anti-phishing policies, set up Safe Attachments and Safe Links, establish data loss prevention rules for sensitive information, and enable audit logging.

Under UK GDPR, email containing personal data must be protected with appropriate security measures. Microsoft 365 Business Premium includes features like email encryption, sensitivity labels, and information barriers that help you meet these obligations. Configure them as part of your migration rather than as an afterthought.