On-Premises Exchange Migration Checklist: What to Check before you Migrate
If your organization still operates on Exchange Server 2016 or 2019, it is time to facilitate the migration. The end of support for the two Exchange Server versions happened on October 14, 2025, meaning that organizations that are not under a support agreement are not able to receive the ‘’usual’’ updates, security patches, and technical support. Following a practical on premises Exchange migration checklist can ensure that the IT teams get rid of any dependencies before they start moving mailboxes, applications, and other users.
The difficult part is rarely the mailbox transfer itself. It is the SMTP relay nobody documented, the application still using EWS, the shared mailbox with complicated permissions, or the directory synchronization issue that appears during a migration batch.
Not sure which path fits your Exchange environment?
Talk to an Exchange migration specialist before you commit to a migration timeline.
What Should your On-Premises Exchange Migration Checklist Cover?
A migration plan should begin with the current environment, not with a target date.
Your first task is to establish exactly what Exchange is doing for the business and which systems depend on it.
Build a Complete Exchange Inventory
Start with the infrastructure and objects that exist today.
- Exchange Server versions, cumulative updates, and server roles
- User, shared, room, resource, and service mailboxes
- Mailbox and archive sizes
- Public folders
- Distribution groups and mail-enabled security groups
- Accepted domains and email address policies
- Send and receive connectors
- SMTP relay servers
- Email security gateways
Do not build this inventory from an old spreadsheet alone. Compare the documentation with the live environment.
Microsoft provides the “Get-ExchangeServer” command to identify Exchange servers and their installed versions.
The useful output from this stage is not simply a server count. It is a dependency map showing what could be affected when Exchange changes.
Identify Every Application That Uses Exchange
This is one of the highest-risk areas in a legacy Exchange migration checklist.
Ask application owners which systems send, receive, or process email through the existing Exchange environment.
Look for:
- ERP notifications
- CRM alerts
- HR systems
- Monitoring platforms
- Backup applications
- Printers and scanners
- Customer portals
- Automated reports
- Internal line-of-business applications
For each application, record the owner, SMTP endpoint, authentication method, sender address, business purpose, and replacement or migration plan.
EWS deserves particular attention. Microsoft has announced that Exchange Web Services will be gradually disabled from Exchange Online starting from 01 October 2026, and it will be fully retired by 01 April 2027. Any organizations that are utilizing EWS should analyze the applications that need to be moved from EWS and get themselves an upgrade.
That makes application discovery more than a migration exercise. It is also a way to avoid carrying an aging dependency into your new environment.
Have applications, SMTP relays, or legacy integrations you are not sure how to handle?
Talk to Evolvous about your Exchange migration
Audit Active Directory and Identity
A move to Exchange Online does not remove identity dependencies. Before migration batches begin, your on-premises Exchange migration checklist should include a detailed review:
- Active Directory health
- User Principal Names
- SMTP addresses
- Microsoft Entra ID
- Microsoft Entra Connect or Cloud Sync
- Duplicate identities
- Group synchronization
- Authentication methods
- Multi-factor authentication
- Conditional Access policies
If Active Directory is still going to play a role in your organization’s architecture, make sure to describe how you are going to manage your recipients after the migration. Microsoft has made sure that enterprises migrating from on-premises Exchange have the chance to keep their existing directory structure intact.
Should you Move to Exchange Online or Stay On-Premises?
While Exchange 2016 and Exchange 2019 have lost support, this does not mean that all enterprises should make the same decision regarding migration.
Microsoft currently provides two broad paths:
- Exchange Online: Transfer data to Office 365, including mailboxes, public folders, and more.
- Exchange Server Subscription Edition: Keep using on-premises Exchange, if necessary, due to several reasons, including business, regulatory, operational, and technical reasons.
Here are several questions to help you decide:
- Is there any regulatory requirement your company needs to comply with regarding where the data is processed or stored?
- Do critical applications require an on-premises Exchange dependency?
- Does the business need extended coexistence?
- Is the IT team prepared to continue operating Exchange infrastructure?
- What is the long-term identity architecture?
- Which option creates the least operational complexity?
The objective is not simply to replace an unsupported server. It is to establish a supported architecture that the IT team can maintain.
Which Exchange Migration Method Fits your Environment?
Once the destination is clear, choose the migration method.
Microsoft documents cutover migration, minimal hybrid migration, and full hybrid migration for organizations moving from on-premises Exchange to Microsoft 365.
Cutover Migration
A cutover approach can suit smaller environments where users can be moved during a concentrated transition.
It works best when the environment has limited coexistence requirements and few complicated dependencies.
Minimal Hybrid Migration
Minimal hybrid can be useful when the organization wants a quick transition while using the Hybrid Configuration Wizard to facilitate mailbox migration. Microsoft positions it for organizations planning to move to Exchange Online over a short period.
Full Hybrid Migration
Full hybrid is designed for environments where coexistence matters.
It can support organizations that need users on both platforms while migration proceeds in stages, with directory synchronization and richer coexistence capabilities.
Do not select a method from mailbox volume alone. Application dependencies, identity architecture, coexistence requirements, network conditions, and the desired end state all influence the decision.
Need help choosing between Exchange Online, hybrid, and an on-premises path?
Discuss your migration strategy with an Exchange consultant.
What Should Be Tested Before the First Large Migration Wave?
A pilot should expose the parts of your environment that a standard mailbox test cannot.
Include users with different:
- Mailbox sizes
- Departments
- Outlook versions
- Mobile devices
- Delegation requirements
- Shared mailbox access
- Calendar dependencies
- Application workflows
Then test:
- Internal email delivery
- External email delivery
- Calendar invitations
- Free/busy information
- Shared mailbox access
- Send As and Send on Behalf permissions
- Outlook connectivity
- Mobile access
- Application-generated email
- Security policies
- Retention and compliance controls
A successful pilot is not one where the team finds zero problems. It is one where the team finds the problems while the affected user population is still small.
Not Sure How Complex Your Exchange Migration Is?
Before you schedule your first migration batch, identify the dependencies that could affect your timeline, mail flow, applications, and user experience.
What are the Biggest Exchange Migration Red Flags?
Some problems deserve attention before the migration schedule is approved.
Unknown SMTP Relays
If nobody can identify which applications use the relay, assume there are undocumented dependencies until proven otherwise.
Unresolved Directory Synchronization Errors
Identity problems can affect provisioning, mailbox matching, and user access.
EWS-Dependent Applications
These need a separate modernization plan because Exchange Online EWS retirement is approaching.
Business-Critical Public Folders
Identify what information they contain, who uses it, and what the target architecture will be before migration.
Missing Application Owners
Every application sending email should have someone responsible for testing and sign-off.
No Post-Migration Validation
A migration batch marked “completed” does not confirm that calendars, permissions, applications, and mail flow are working correctly.
Need a Migration Roadmap?
Get a tailored Exchange-to-Microsoft 365 migration roadmap
Is Your Exchange Environment Ready for Migration?
A good on-premises Exchange migration checklist should help your IT team answer a more important question than “Have we moved all the mailboxes? From Exchange discovery and dependency mapping to migration strategy, Microsoft 365 readiness, testing, and decommissioning, each stage needs careful planning to avoid disruption.
With Evolvous, IT teams can assess their existing Exchange environment, identify migration risks, choose the right migration approach, and build a practical roadmap for moving to a supported architecture. Whether you are planning Exchange Online migration or evaluating your on-premises options, talk to Evolvous your Exchange migration consultant about your Exchange migration and take the next step with a plan built around your environment.
Frequently Asked Questions
1. What is the biggest risk in a legacy Exchange migration?
Treating the project as a mailbox transfer. Mail flow, identity, application integrations, shared mailboxes, permissions, public folders, and compliance requirements can all affect the outcome.
2. What should organizations do about EWS before migrating to Exchange Online?
Identify applications using EWS and plan their modernization. Microsoft has scheduled phased EWS disablement in Exchange Online from October 1, 2026, with full retirement on April 1, 2027.
3. Should every organization move directly to Exchange Online?
No. Exchange Online is a common destination, but organizations with specific operational or technical requirements can evaluate Exchange Server Subscription Edition as an on-premises option.
