Thunderbird 154 Adds Microsoft Graph Support for Microsoft 365 Accounts

Thunderbird 154 is now available, and this release brings a much-anticipated feature for professionals: support for Microsoft Graph for Microsoft 365 accounts. It arrives just in time, as Microsoft is preparing to block EWS in a few weeks. Here is the essential information you need to know about this new release.

Microsoft Graph enabled, but only for email

The new version of Mozilla Thunderbird released on August 18, 2026 mentions this: Microsoft Graph enabled for Microsoft 365. Behind this line lies work that has been underway for several months at Mozilla. After the arrival of native Exchange Web Services support in Thunderbird 145, the email client can now communicate with the API that is meant to replace EWS in Microsoft’s cloud.

Be careful, though, as Mozilla explains, there are a few limitations to be aware of:

• Microsoft Graph support in Thunderbird is limited to email. The calendar is not supported yet.
• Graph is only available on Microsoft 365. On-premise Exchange servers must continue using IMAP or EWS. That is expected, as this API is limited to Microsoft’s cloud.
• Setup is done through Thunderbird’s account manager. You must select the "Graph" protocol in manual mode, then enter https://graph.microsoft.com/ as the endpoint and choose OAuth2.

Mozilla includes a warning on the page: Graph support is recent and bugs may still remain. In other words, test it before rolling it out broadly.

Thunderbird 154 delivers a long-awaited feature, and time is running out. Starting on October 1, 2026, EWS requests will be blocked by default on Exchange Online tenants that have not configured an allow list and set the EWSEnabled parameter to True. The final shutdown is scheduled for April 2027, as we detailed in our article about the Exchange Web Services deprecation announced by Microsoft.

Other new features in Thunderbird 154

Beyond Microsoft Graph support, Thunderbird 154 brings other improvements. Notably, there is a new optional mode: once enabled, the application stays open even if you close the last window. It remains accessible from the notification area via an icon, on Linux and Windows.

The other changes listed by Mozilla are more targeted:

• A new setting allows global search results to open in list view by default.
• Attachments of type message/rfc822 gain a "Copy to" entry in their context menu and can be dragged directly into the folder tree.
• On macOS, an attachment preview is now available.

This release also fixes several IMAP bugs. The most notable one concerns moving IMAP folders to local folders: if the copy failed, messages could be deleted. That is now fixed. Another fix addresses empty IMAP attachments after a filter-based move.

The remaining bug fixes concern integration with Microsoft tools and calendars:

• Exchange accounts could repeatedly report false authentication failures.
• Custom OAuth settings for an EWS account were overwriting those of the original account.
• The DisablePasswordReveal policy did not actually prevent saved passwords from being displayed.
• CalDAV synchronization failed when the server responded in UTF-16.
• A dismissed CalDAV reminder could permanently block subsequent notifications.
• Read-only CardDAV address books were treated as editable.

After Thunderbird 151 and Thunderbird 153, this version 154 confirms the direction Mozilla is taking: making the open source client a credible alternative to Outlook in Microsoft 365 environments. You can find the release notes on the Mozilla Thunderbird website.

Florian Burnel Co-founder of IT-Connect

Systems and network engineer, co-founder of IT-Connect and Microsoft MVP "Cloud and Datacenter Management". I'd like to share my experience and discoveries through my articles. I'm a generalist with a particular interest in Microsoft solutions and scripting. Enjoy your reading.

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