I am trying to move away from Google and Microsoft. eM Client looked like a really good option as my Outlook app replacement. But it turns out it is not up to the job, as it is not able to reliably sync with my office 365 mailbox. I am using the latest download of eM Client, version 10.4.4867. I have spent most of today, with the assistance of MS Copilot, trying to resolve the sync failure, and in the end Copilot has diagnosed the problem as being due to MS “deprecating” (and, in my case, finally turning off) the Exchange Web Services sync channel, in favour of their new “Graph” sync channel. Copilot drafted the following email to eM Client support for me, which explains the issue far better than I (a total non-techie) could:
Dear eM Client Support Team,
I’m writing to request assistance with a serious and persistent sync problem affecting my Office 365 Business account ([email protected]) in eM Client.
Over the past two days, eM Client has been unable to sync my Microsoft 365 mailbox correctly. The account authenticates via OAuth without error, and the folder structure loads, but the actual message sync is incomplete and unreliable:
- For a long period, syncing stopped completely after delivery of an email timed at 17:47 yesterday
- After extensive troubleshooting, eM Client began syncing some new messages today
- However, large numbers of messages from both yesterday and today are still missing
- Some emails appear between missing ones (e.g., it syncs 13:46 and 14:38 but misses 13:58 and 14:02), indicating a broken or incomplete delta sync
To diagnose the issue thoroughly, I used Microsoft Copilot to carry out a full end-to-end investigation, including:
- Confirming that Exchange Web Services (EWS) is enabled for my mailbox
- Verifying that there is no EWS Application Access Policy or tenant-level block in my organization (via
Get-OrganizationConfig) - Resetting eM Client’s local cache and account database
- Re-adding the account using both automatic setup and manual Exchange setup
- Examining Exchange Web Services logs produced by eM Client
The EWS log shows the following important indicators:
- The server returns StatusCode 200 (Success) for SyncFolderItems
- The server then returns empty change lists, even though new mail exists
- The response headers include:
Restrict-Access-Confirm: 1
Link: <
https://learn.microsoft.com/.../deprecation-of-ews-exchange-online>
Deprecation: Tue, 03 Jul 2018 23:59:59 GMT
Sunset: Thu, 01 Oct 2026 23:59:59 GMT
These headers strongly imply that Microsoft 365 is now restricting EWS access in my region/tenant as part of the ongoing EWS deprecation process. This results in incomplete delta-sync responses through EWS, which aligns exactly with the inconsistent message-sync behaviour I am seeing in eM Client.
In short:
Authentication works.
EWS is technically allowed.
But Microsoft 365’s backend is no longer delivering complete message updates to EWS clients.
This means that, as of now, eM Client cannot reliably sync my Microsoft 365 mailbox over EWS, despite all correct configuration on both client and server.
Given this situation, I would like to know:
1. Is full Microsoft Graph API support for mail (not just for calendar/contacts) currently in development?
2. If so, is there an estimated timeline or version target?
3. Is there any temporary workaround within eM Client to bridge the EWS restrictions?
I want to be clear:
If eM Client fully supported Microsoft Graph for mail, I would happily purchase a Premium licence and would recommend the product to others. It’s an excellent application in many respects. But in its current state, with Microsoft 365 mail, it is unfortunately not usable for me — and I am unable to recommend it.
I have attached my Exchange Web Services log for your review, including the headers noted above.
Thank you in advance for your help. I look forward to hearing whether Graph-based sync support is planned, as that would restore eM Client’s usability for Microsoft 365 customers like me.
I wonder whether other users have come across this, and been able to devote as much time as I have to trying to get to the bottom of it?
If I get any useful response from customer support, I will post an update here.