EWS Retirement Enters Its Final Stage: What MigrationWiz Users Should Know

What Is EWS and Why Is Microsoft 365 EWS Retirement?

Exchange Web Services (EWS) is a Microsoft technology that allows applications to work with Exchange mailbox data. It has been widely used to access emails, calendars, contacts, and other mailbox information. 

Microsoft is gradually moving Exchange Online toward newer APIs and technologies. Because of this change, EWS is being retired in stages rather than being switched off all at once.

The final phase brings tighter control over applications that still need EWS access. Microsoft has introduced EWSAllowedAppIDs to help administrators manage this access. For migration teams, this means EWS settings should now be checked as part of the normal migration preparation process.

What Is EWSAllowedAppIDs?

EWSAllowedAppIDs is an allow list that Microsoft 365 administrators can use to specify which applications are permitted to access EWS. In simple terms, an administrator can identify an approved application by its Application (client) ID and add that ID to the tenant’s EWS allow list.

This is crucial to MigrationWiz users because when performing migrations based on EWS, you might require the application ID used in the authentication of Microsoft 365. It also helps give more control to administrators concerning third-party applications trying to access Exchange Online.

What MigrationWiz Users Need to Do

1. Set up Modern Authentication fully: Sign in and configure the required Microsoft 365 app needed for migration.
2. Find the Application (Client) ID: This is the ID for the registered app used for authentication purposes.
3. Add the App ID to EWSAllowedAppIDs: Add the required application ID to the Microsoft 365 tenant’s EWS allow list.
4. Check the configuration: Make sure the correct App ID has been added and there are no typing errors.
5. Wait for some time to get it done: It is better to wait and not make changes before migration.
6. Test the connection: Run a test before moving the complete set of mailboxes.

Why the October 1, 2026 Deadline Matters

The October 1, 2026 date is an important point in the Exchange Online EWS retirement timeline. Microsoft is introducing stricter EWS access rules for tenants that continue to have EWS enabled but do not configure the required application allow list.

Once the new behavior applies to a tenant, applications that are not included in the allowed list may no longer be able to use EWS. For this reason, migration teams should not wait until the deadline is close. If a migration is planned for the coming months, EWS configuration should be reviewed during the planning stage.

Microsoft has also been communicating the upcoming changes through the Exchange Team. The earlier article Exchange Online EWS, Your Time is Almost Up provides additional background on the retirement.

Allow Time for Microsoft 365 Changes

One point that migration administrators should keep in mind is that configuration changes may not become active immediately. Therefore, adding an App ID just before a migration is not a good idea. After making the change:

• Verify that the App ID is present.
• Record the current allow-list configuration.
• Give Microsoft 365 enough time to apply the change.
• Test the migration connection.
• Run a small migration before starting the full project.

Take a Backup Before Starting the Migration

EWS configuration is only one part of migration preparation. In addition to that, it would be prudent to maintain a duplicate copy of the relevant mailbox data before undertaking significant modifications to the Microsoft 365 environment. The backup will come in handy in situations where certain items are skipped during the migration process, or the migration process gets stalled halfway.

The SysInfo Office 365 Backup Tool can be considered as part of a pre-migration backup plan. The tool is designed to back up Office 365 mailbox data and save it in formats such as PST, PDF, EML, MBOX, and CSV. It can be useful for:

• Support for large Office 365 emails, contacts, and calendars with accuracy.
• Features like Remove Duplicate, Date Filter, Attachment handling, and more.
• Secure authentication mode using Modern or Admin Impersonation.
• Maintains the original email formatting structure and metadata.
• Highly compatible with all Windows, Mac, or Linux versions.

Why You Should Test Before the Migration

A full mailbox migration can involve hundreds or thousands of users. Discovering an Exchange Web Services retirement or authentication problem after the migration has started can cause unnecessary delays. A small test migration gives administrators a chance to check:

• Microsoft 365 authentication
• EWS access
• Application permissions
• EWSAllowedAppIDs configuration
• MigrationWiz endpoint settings
• Mailbox access
• Folder and message migration

Final Words

Microsoft’s EWS retirement is an important change for organizations planning Exchange Online migrations with MigrationWiz. The introduction of EWSAllowedAppIDs gives administrators a way to control which applications can continue using EWS during the transition. Before starting a migration, review the tenant’s EWS settings, complete the required authentication setup, identify the correct Application ID, configure the allow list where required, and test the connection.

It is also sensible to back up important mailbox data before the full migration begins. A separate backup can provide an extra layer of protection if the migration is interrupted or some data needs to be checked later. Most importantly, do not leave EWS preparation until the migration day. Review the environment early, test with a smaller mailbox set, and keep your configuration documented.

Frequently Asked Questions

About The Author:

Simran Bhatia

Simran Bhatia is a technical content writer engaged in writing clear, concise, and SEO-optimized content. With a background in computer science and a passion for writing, I thrive to deliver complex technical content in simple layman terms.