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Thunderbird Desktop New Protocol Support: Microsoft Graph API

As many of you know, Microsoft will be disabling Exchange Web Services (EWS) support on its Microsoft 365 platform later this year. The Thunderbird Desktop team has been hard at work to ensure continuity of functionality through this transition, and today we are pleased to announce the release of native Thunderbird support for the Microsoft Graph API! Curious what this means for you? Then keep reading to find out!

IMAP and EWS and Graph, Oh My!

When connecting to either on-premises or hosted Microsoft accounts, Thunderbird users now have an array of options. Users might not know which option is best for their case, so we’ll start with a little bit of guidance to help users decide what will be best for them. First off, if you are currently using IMAP with an on-premises Exchange account or a Microsoft 365 hosted account, and it’s currently working for you, then there’s nothing you need to do! EWS and Graph support are for users whose organizations do not allow IMAP access.

Now for the more complicated part. Last year, we released EWS email support for both on-premises Exchange accounts and Microsoft 365 hosted accounts. If you are using the EWS protocol with an on-premises Exchange account, then you don’t need to do anything.

However, if your organization uses Microsoft 365 for email, and you’re currently using EWS to connect to that account, then you need to take action before October of this year. Earlier this year, Microsoft announced that they would begin a phased shutdown of EWS on Microsoft 365/Exchange Online starting in October of 2026 with the goal of a complete shutdown in 2027. If you are currently using Thunderbird’s EWS support to connect to a Microsoft 365/Exchange Online email account, then you will need to switch to the Microsoft Graph API support to keep using Thunderbird beyond these dates. See below for details.

So the TL;DR is:

• IMAP for on-premises or Microsoft 365 hosted email => No action required.
• EWS for on-premises Exchange => No action required.
• EWS for Microsoft 365/Exchange Online => Set up a new Microsoft Graph account in Thunderbird.

Microsoft only supports the Graph protocol on Microsoft 365, so that is the only provider that offers it. On-premises Exchange servers do not implement the Graph API, so Thunderbird’s EWS support will continue to be the primary mechanism for users on these servers to connect to their email accounts.

Microsoft Graph Account Set Up

Thunderbird does not support migrating accounts to different protocols. Instead, you will need to set up a new account. If you have an existing EWS-connected Microsoft 365 account, first you’ll need to delete that account in Thunderbird. You can do this from the account settings. Deleting the account locally in Thunderbird will not affect any data stored on Microsoft 365, so your data is safe.

Once your previous EWS account has been deleted, you can use Account Hub to set up a new account. In the new account set up dialog, enter your Microsoft 365 hosted email account. Thunderbird should automatically detect that your email is hosted on Microsoft 365 and will give you a few options for getting connected. Choose the Microsoft Graph option, and you should be good to go! If for some reason automatic configuration doesn’t work, you can still configure your account manually using these instructions.

What is currently supported?

As with EWS, Thunderbird’s current Graph support extends only to email. Thunderbird does not yet support Calendar and Address Book functionality with either EWS or Graph.

What’s in ESR?

Thunderbird’s current Extended Support Release, version 153, supports the EWS protocol, but does not support the Microsoft Graph API, which was first enabled in the Thunderbird Release channel in version 154. Users on the ESR channel who are using Microsoft 365 will need to migrate to the Release channel in order to use the Microsoft Graph API support to continue accessing Microsoft 365 hosted mailboxes.

What’s Next?

Calendar and Address Book! The Thunderbird Desktop team has already started working on support for connecting to Microsoft 365-hosted calendars using the Graph protocol. We will be busily working on this throughout the rest of the year. As with our previous work on Thunderbird support for EWS, this is the first new calendar protocol to be added to Thunderbird in many years. We are currently doing some up-front design work to ensure a sustainable product going forward and hopefully make the next calendar protocol easier to add.

How can users give us feedback?

As with all new functionality, there may be features we are missing or unexpected issues. As always, Bugzilla is always open! You can send us feature requests and issue reports using this Bugzilla link. Thunderbird’s greatest strength is its community of users, developers, and supporters who help us deliver the best tools we can to connect people with one another. We welcome community involvement to help us make everything better!

Nitty-Gritty development details

Those of you who have followed along with development throughout EWS and into Graph support might have noticed that, compared to EWS, we were able to implement support for the Microsoft Graph API relatively quickly. This is largely due to the up-front thought and work that went into the design and development of Thunderbird’s EWS support. The Graph implementation was the team’s first test of the extensibility of the new architecture, and we were very pleased with the results. It took 11 months to enable basic synchronization with EWS. With the new architecture, we were able to cut that time down to 4 months with Graph.

Graph’s operations are similar to the operations that EWS provides, but different enough that it served as a great first test case for how the new email client architecture can support future protocols, such as JMAP. Given the results of the Graph implementation, we are optimistic that the same architecture will extend to JMAP once the team decides to move forward to that new protocol. We are hopeful that what we have built here can provide a sustainable base on which to build future protocol support in Thunderbird.

This would not have been possible without many contributions from Thunderbird developers, past and present, and the community of users who have helped us improve Thunderbird by submitting issue reports and feature requests. We are grateful to everyone for their support!