Dynamics 365 on-premise and the end of Exchange Web Services

If you run Dynamics 365 on-premise and your mailboxes are in Exchange Online, the link between the two is going to stop working. This article explains what is changing, when it happens, and what you can do about it.

What is changing

Dynamics 365 on-premise, like Dynamics CRM before it, uses server-side synchronisation to keep email, appointments, contacts and tasks in step with Exchange. When the mailboxes are in Exchange Online, server-side synchronisation reaches them through an interface called Exchange Web Services, or EWS.

Microsoft is removing EWS from Exchange Online. It stopped adding features to EWS in 2018, and in 2023 it set the date for switching it off. Applications are expected to use the Microsoft Graph API instead. Microsoft’s own account is in Deprecation of Exchange Web Services in Exchange Online.

Microsoft is not moving the on-premise product to Graph. Its guidance for Dynamics 365 on-premise says the connection to Exchange Online gets no further updates and will be removed.

The dates

These are the dates Microsoft has published. They were correct when this article was written, so check the two pages above before you plan around them.

• 25 May 2026. Support ended for Dynamics CRM on-premise version 8.0 with Exchange Online.
• 1 October 2026. EWS starts to be disabled in Exchange Online, for every organisation. This is Microsoft’s recommended deadline for moving to Dynamics 365 Online. An organisation that is not ready can keep EWS until the final date by being added to an allow list.
• 1 April 2027. EWS is fully disabled. Support ends for Dynamics 365 on-premise version 9.0 with Exchange Online.

If your synchronisation is still working today, it is because EWS is still switched on for your organisation. It will not be after 1 April 2027.

What stops working

When EWS is switched off for your organisation, server-side synchronisation between Dynamics 365 on-premise and Exchange Online stops. In practice:

• Email arriving in a user’s mailbox or a queue’s mailbox is no longer tracked in Dynamics.
• Email written in Dynamics is no longer sent through the mailbox.
• Appointments, contacts and tasks no longer synchronise between Dynamics and Outlook.

Dynamics itself carries on working, and so does Exchange Online. It is only the link between them that is lost.

Your three options

1. Move to Dynamics 365 Online

This is Microsoft’s recommendation, and for most organisations it is the right place to end up. It is also a project. Customisations, integrations, reports and data all have to be moved and tested, and the licensing is different. For a large or heavily customised system, that may not be finished by April 2027.

We do this work. See what we do on Dynamics 365.

2. Use Exchange Server on-premise

Microsoft lists this as the alternative: connect Dynamics 365 on-premise to a supported on-premise version of Exchange Server. It suits an organisation that still runs Exchange Server. If your email has already moved to Exchange Online, it means moving mailboxes back, which few organisations will want to do.

3. Stay on-premise and replace the synchronisation

This is what Prism Email Router is for. We should say plainly that it is our own product.

Prism Email Router connects Dynamics 365 on-premise to Exchange Online through the Microsoft Graph API, so it does not depend on EWS.

• Emails, appointments, recurring appointments and tasks synchronise both ways. Service appointments and phone calls are pushed from Dynamics into Outlook.
• It works with user mailboxes and queue mailboxes.
• Nothing changes inside Dynamics. There are no schema changes and no customisations.
• It runs on your own server, so your mailboxes and your CRM data stay inside your infrastructure.
• It supports Dynamics 365 Customer Engagement on-premise and Dynamics CRM 2016, 2015 and 2013.

It is meant to give you time. It keeps an on-premise system working with Exchange Online until you are ready to move to Dynamics 365 Online.

What to do now

1. Find out which version of Dynamics you run, and whether its mailboxes are in Exchange Online.
2. Ask whoever administers Exchange Online whether EWS is still switched on for your organisation, and until when.
3. Decide where you want to be. If a move to Dynamics 365 Online cannot be finished before April 2027, plan for something to cover the gap.
4. Test before the deadline, not after it. You can request a trial of Prism Email Router on the product site.

If you would like to talk it through, get in touch.