Support and setup

M365 Reactions displays Microsoft 365 Outlook email reactions inside Thunderbird, including emoji, counts, and the names of people who reacted.

Thunderbird 140+ Microsoft 365 mailbox Microsoft Entra application

About the add-on

The add-on uses Microsoft Graph to find the exact Outlook message by its RFC Message-ID. It then reads Outlook's reaction properties using delegated Exchange mailbox access because those properties are not included in normal IMAP messages or the Microsoft Graph message response.

Each Microsoft 365 mailbox must be connected separately. Multiple Thunderbird accounts are supported.

Important: The add-on can display existing reactions, but it cannot create, change, or remove them because Microsoft does not provide a supported Outlook reaction write API. Use Open Outlook to react to open the exact message in Outlook on the web.

Setup instructions

The Entra registration and admin consent steps normally need to be completed by your Microsoft 365 administrator.

Part 1Register the Microsoft Entra application

  1. Open the Microsoft Entra admin center.
  2. Go to Identity → Applications → App registrations → New registration.
  3. Name the application Thunderbird M365 Reactions.
  4. Select Accounts in this organizational directory only, unless the same registration needs to be used across multiple Microsoft 365 tenants.
  5. Leave the redirect URI blank on the initial registration screen, then select Register.
  6. On the application overview page, copy the Application (client) ID and Directory (tenant) ID. You will enter both in the add-on later.
  7. Install the add-on using Part 2 below. Open its preferences and copy the displayed Entra SPA redirect URI.
  8. Return to the Entra application and open Authentication → Add a platform → Single-page application.
  9. Paste the exact redirect URI shown in the add-on and save it. Allow public client flows is not required and can remain disabled.

Add the required delegated permissions

  1. Open API permissions → Add a permission → Microsoft Graph → Delegated permissions.
  2. Add Mail.Read and User.Read.
  3. Select Add a permission again, then choose APIs my organization uses.
  4. Search for Office 365 Exchange Online, choose Delegated permissions, and add EWS.AccessAsUser.All.
  5. Select Grant admin consent for the configured permissions.

Required delegated permissions

  • Microsoft Graph: Mail.Read
  • Microsoft Graph: User.Read
  • Office 365 Exchange Online: EWS.AccessAsUser.All
Do not create a client secret. A Thunderbird add-on is a public client and cannot securely protect one. Authentication uses the authorization-code flow with PKCE.

Part 2Install the Thunderbird add-on

  1. Open Thunderbird and select Add-ons and Themes.
  2. Open the gear menu and select Install Add-on From File….
  3. Select the downloaded m365-reactions-thunderbird.xpi file and confirm the installation.
  4. Open the M365 Reactions add-on's Preferences.

Part 3Connect each Microsoft 365 account

  1. In the add-on preferences, enter the Directory (tenant) ID and Application (client) ID created in Part 1.
  2. Select Save, then select Connect Microsoft account.
  3. Complete both Microsoft authorization windows. One authorizes Graph message lookup and the other authorizes access to the Exchange reaction properties.
  4. Confirm that the connected Microsoft email address matches the mailbox used by that Thunderbird account.
  5. Repeat these steps for every additional Microsoft 365 account configured in Thunderbird.

Using the add-on

Troubleshooting

No reactions appear for a message

Confirm that the same message shows reactions in Outlook on the web, that the correct Microsoft account is connected in the add-on preferences, and that Thunderbird is version 140 or newer. Use the refresh button in the Reactions popup to bypass the five-minute cache.

Microsoft asks me to sign in again

Microsoft limits refresh tokens issued to browser-based SPA clients. If interaction is required again, open the add-on preferences and select Connect Microsoft account to renew the session.

I cannot add or change a reaction

This is a Microsoft API limitation, not an installation problem. Select Open Outlook to react and change the reaction in Outlook on the web.

Thunderbird reports unrestricted access

Message-list reaction pills use a bundled Thunderbird Experiment because the standard MailExtension API cannot decorate message card rows. The Experiment injects the reaction pills and their stylesheet into Thunderbird's message-list view.

The add-on will not install

Confirm that Thunderbird 140 or newer is installed. Private unsigned builds may require temporary loading or signing depending on the Thunderbird release channel and your organization's add-on policy.

Technical limitations and data storage