Information checked: 21 July 2026.
Microsoft 365 can combine Exchange Online email with calendars, Office applications, Teams and document services. The correct plan depends on whether the business needs only cloud services, desktop applications, device management or additional security controls.
In brief: Plan Microsoft 365 as an identity and collaboration system, not only a place to point the domain’s MX record.
Choose the service by workload
| Need | What to check | Why it changes the plan |
|---|---|---|
| Business email | Mailbox size, shared mailboxes and archiving | Email-only requirements may not justify desktop apps |
| Desktop Office apps | Install rights and device limits | Some business plans provide web/mobile apps only |
| Teams and collaboration | Meeting, chat and file workflow | Packaging can vary by market and plan |
| Device and identity controls | Conditional access and device management | Security features differ substantially |
| Retention and legal needs | Policies, eDiscovery and audit requirements | May require specialist licensing and configuration |
Add the custom domain without breaking mail
Microsoft supports Domain Connect with participating registrars or manual DNS setup. Verify ownership and create users before switching MX. Incorrect DNS records can interrupt mail and other services, so export the current zone and confirm every record before changing it.
Design accounts and shared addresses
Create named identities for people. Use aliases, distribution lists or shared mailboxes for team addresses according to the workflow. Keep at least two protected administrative accounts and document who can recover the tenant.
Acceptance test
- Test inbound and outbound mail with several external providers.
- Check shared mailbox access, Send As behaviour and replies.
- Confirm SPF, DKIM and DMARC results.
- Test Outlook, web and mobile access for representative users.
- Complete one account offboarding exercise, including files and licences.
- Record domain, tenant, billing and support ownership.
Do not treat migration as a DNS-only task
Historical mail, calendars, contacts, shared mailboxes, mobile profiles and application senders may all need migration. Establish coexistence or a clear cutover window and retain the old service until records are reconciled.
Example: mailbox migration without collaboration migration
Mail may arrive after the MX switch while shared calendars, Teams links, mobile profiles and files still point to the old system. Users then report a mixture of missing history and duplicate identities. The cutover plan should list every workload and provide a clear support route for the first working days.
What the business should retain
- Tenant ID and domain ownership
- Licence and user register
- Shared mailbox and group map
- Migration reconciliation report
- Administrator recovery and offboarding steps
Sources and date checked
Technical and product information was checked against the following primary sources on 21 July 2026. Plans, interfaces and provider terms can change, so recheck them before purchase or migration.
Keep the decision under your control
Retain the relevant accounts, source material, supplier terms and recovery information. Recheck changing prices, interfaces and rules before acting.