eM Client and Thunderbird: ready for the EWS shutdown?

Short answer: Both have a Graph version now: eM Client 11 (version 10 and older use EWS) and Thunderbird 154 (mail only, no calendar over Graph yet). Update, then re-add the account with Microsoft Graph if the client asks.

✔ Has a Microsoft Graph version · vendor statements checked 26 Oct 2026

Deadline: Exchange Online blocks EWS by default from October 2026 (tenants are switched to EwsEnabled False, rollout to late April 2027) and turns it off for good on 1 April 2027, with no exceptions. Exchange Server on-premises is not affected.

Status

eM Client: Graph in version 11. Thunderbird: Graph in 154, mail only.

This vendor registers its own app in each tenant, so the app ID is yours. Find it in the EWS usage report, or run the free script with -ResolveNames.

What to do

  1. Update eM Client to 11, or Thunderbird to 154 or later.
  2. Re-add or convert the Microsoft 365 account to the Graph protocol.
  3. Thunderbird users who need the calendar: plan another route (for example the new Outlook) before 1 April 2027.

More than one app? Run the free read-only script: it names every app still calling EWS in your tenant.

Allow-list it safely

Setting EwsAllowedAppIDs replaces the whole list, so adding one ID on its own removes every other app. Read the current list first, then write the merged list:

Get-OrganizationConfig -RetrieveEwsOperationAccessPolicy | Format-List EwsEnabled,EwsAllowedAppIDs
Set-OrganizationConfig -EwsEnabled $true -EwsAllowedAppIDs "<current IDs>,<new ID>"

Changes to the list take up to 24 hours. A blocked call returns HTTP 403 with the header X-EWS-Policy-Reason. The free script prints the merged command for every app in use (it never runs it).

Sources

MSP or IT partner? The M365 Readiness Pack runs this EWS check, the SMTP AUTH check and SPF/DKIM/DMARC for every domain once per client tenant, and writes a client-ready report with your logo, next steps and an email to send the client. Read-only, works with GDAP.

See the pack (from $49)
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