Microsoft Is Discontinuing Its Exchange Web Services (EWS) for Microsoft 365: What Does This Mean for MailStore Customers?

Microsoft has announced that it will no longer support Exchange Web Services (EWS) for Exchange Online as of October 1, 2026. This decision affects all companies that use EWS in combination with Exchange Online (Microsoft 365) – and thus numerous third-party solutions.
The good news is that with MailStore, you are well prepared for the changeover.

What Exactly Are Exchange Web Services and What Are They Used for?

EWS is an older technology that was developed specifically for accessing Exchange data. The API enables access to data from Microsoft Exchange Server and Exchange Online, including emails and mailboxes. EWS has been a central interface for third-party solutions such as archiving systems.

What Will Happen in October?

Microsoft plans to disable EWS for Exchange Online starting October 1. This decision will force manufacturers to switch to the Microsoft Graph API.
Microsoft Graph is the modern interface for the entire Microsoft 365 world – from Outlook to Teams to OneDrive. This API enables access to resources and services within Microsoft 365 and serves as a central interface for integrations.

What Will Change for MailStore Server and the MailStore SPE?

The shutdown of EWS initiated by Microsoft will require adjustments to MailStore Server and the MailStore SPE, depending on the settings in the archiving solution.
This is because archiving methods within MailStore Server and MailStore SPE that were previously controlled via EWS will no longer be available from October 1 and will then run into errors. This affects the MailStore customers listed below. Customers who use MailStore Cloud are not affected by the shutdown of EWS.

The following settings are expected to be affected in detail from October onwards:

• Importing Exchange Online mailboxes
• Importing Exchange Online archive mailboxes
• Importing Exchange Online public folders
• Exporting emails to Microsoft 365 (bulk export)

Your Next Steps for a Secure Transition

To ensure you are well prepared for the transition, we have compiled a few recommendations below:

• Replace public folders with group mailboxes (if available) in good time (see Microsoft recommendation). We will provide updates on this, but until then there is no urgent need for you to take any action. Keep an eye on our blog .
• We will support you: We will provide instructions and tools in good time to help you convert your EWS-based archiving profiles. Until then, you don’t need to do anything yourself.
• Plan the migration of Exchange Online archive mailboxes to Mailstore – ideally before October to ensure a smooth process.
• Please note: If you use Exchange Online Kiosk, Microsoft Office 365, and Office 365 F1/F3, you should make the change by June. Further information can be found here.
• We will keep you up to date: We will publish regular announcements to make the transition as easy as possible for you. Feel free to follow our blog, release announcements, and, of course, the changelog.

And don’t forget: Keep your MailStore version up to date. Regular updates ensure that you benefit from new features and that your software is always up to date.

The first adjustments will be made in the upcoming release 26.1 in mid-January. As usual, we will inform you about all changes in MailStore in our changelogs.