Exchange Server to Microsoft 365 Migration Checklist

Moving from on-premises Exchange Server to Microsoft 365? Use this checklist to assess server health, identity, mailboxes, shared mailboxes, public folders, applications, security, DNS and cutover before decommissioning Exchange.

Business Case

• □ Define the reason for migration (end of support, cost, cloud strategy)
• □ Identify the executive sponsor
• □ Confirm critical dates and dependencies
• □ Record contractual obligations and compliance requirements

Source Server Health

• □ Confirm Exchange Server version (2016, 2019 or other)
• □ Review Windows Server version and patch level
• □ Check available disk space and CPU load
• □ Review event logs for recurring errors
• □ Confirm database health and replication status
• □ Record any existing connectors and transport rules

Tenant Ownership

• □ Confirm Microsoft 365 Global Administrator access
• □ Confirm domain and DNS control
• □ Verify target Microsoft 365 licensing plan
• □ Record delegated supplier responsibilities

Identity

• □ Confirm whether Active Directory is in use
• □ Confirm Microsoft Entra Connect (or Entra Cloud Sync) status
• □ Inventory on-premises user accounts to be migrated
• □ Inventory external contacts and distribution lists
• □ Map on-premises UPNs to Microsoft 365 sign-in addresses
• □ Confirm password synchronisation or pass-through authentication method

Mailboxes

• □ Inventory all user mailboxes and measure size
• □ Identify large mailboxes requiring staged migration
• □ Record archive mailboxes
• □ Review mailbox permissions (Send As, Send on Behalf, Full Access)
• □ Identify litigation holds and retention policies
• □ Confirm target Exchange Online plan supports required features

Shared Mailboxes

• □ Inventory all shared mailboxes
• □ Record shared mailbox permissions
• □ Identify which users require access after migration
• □ Confirm shared mailbox licensing requirements

Public Folders

• □ Inventory public folders and measure total size
• □ Review public folder permissions
• □ Decide whether to migrate or replace public folders (Teams, SharePoint)
• □ Test public folder access during the pilot

Applications and SMTP Relay

• □ Inventory line-of-business applications that send or receive email
• □ Identify printers, scanners and devices using SMTP relay
• □ Plan replacement SMTP relay for each application or device
• □ Record application dependencies on Exchange Web Services (EWS)
• □ Test application mail flow before cutover

Security

• □ Enable multi-factor authentication for all migrated accounts
• □ Configure Microsoft Defender for Office 365 or equivalent
• □ Review and configure anti-spam and anti-malware policies
• □ Confirm Microsoft 365 backup or retention is in place
• □ Remove or restrict on-premises administrator accounts post-migration

Email Authentication and DNS

• □ Plan MX record cutover timing
• □ Configure SPF record for Microsoft 365
• □ Configure DKIM signing in Exchange Online
• □ Configure DMARC policy
• □ Remove or update legacy SPF entries for on-premises Exchange
• □ Confirm Autodiscover DNS record update

Pilot

• □ Select representative pilot users across departments
• □ Migrate pilot mailboxes and test mail flow
• □ Test calendar, contacts and shared mailbox access
• □ Test public folder access if retained
• □ Confirm Outlook, OWA and mobile client connectivity
• □ Gather feedback and resolve issues before full cutover

Cutover

• □ Confirm cutover date and communicate to all users
• □ Update MX records to point to Exchange Online
• □ Update Autodiscover DNS record
• □ Confirm all in-flight messages are delivered
• □ Update SMTP relay settings for applications and devices
• □ Remove on-premises Exchange from send connectors

Validation

• □ Confirm mail flow in and out of Exchange Online
• □ Test shared mailboxes and calendar permissions
• □ Test public folders or replacement solution
• □ Confirm application and SMTP relay mail flow
• □ Test backup and restore
• □ Run Microsoft 365 mail flow reports

Decommissioning

• □ Confirm no mail is queued on the on-premises server
• □ Preserve backup of Exchange databases before decommissioning
• □ Remove or disable Exchange Server following Microsoft guidance
• □ Remove on-premises Exchange objects from Active Directory cleanly
• □ Obtain written sign-off before server retirement
• □ Document final state for compliance records