Microsoft has changed the account authorization process for its email platforms. As a result, the Mozilla Thunderbird client and other email apps may have trouble logging into your Outlook, Hotmail, or Live addresses. Affected users can take a few steps to try and resolve the issue while Mozilla searches for a permanent fix.

This is an odd mess. Essentially, Microsoft-owned email addresses no longer support basic authentication. Third-party clients like Thunderbird can still log in to Microsoft services, but only through OAuth. It’s a good security measure—OAuth prevents a client like Thunderbird from “seeing” your Microsoft login credentials—but Microsoft’s new OAuth implementation doesn’t recognize Thunderbird as a desktop email client.

Mozilla is working to resolve the problem. Presumably, Thunderbird needs a new OAuth setup with advanced MFA support. In the meantime, Thunderbird users must go down a circuitous route to receive emails from their Outlook, Hotmail, and Live inboxes. The steps are outlined in a Mozilla support post and in several Reddit threads, but we’ll give you the gist of it here.

Open the Advanced Security section of your Microsoft account (Outlook, Hotmail, or Live) and enable two-step verification. Once that’s done, you’ll see an “App Passwords” section on the Advanced Security page. Click the “create a new App Password” button. This will generate a new App Password, which you don’t need to copy-paste. Close the web page if you want.

In the Thunderbird client, open Account Settings and click the “Server Settings” button under your Microsoft email address. Set the authentication method to OAuth2 and click “Done.” A Micorosft pop-up should appear on your screen—enter your Microsoft password (as opposed to the App Password you generated), and Microsoft will ask if you want to let Thunderbird access your account. Click the “Accept” button, and Thunderbird will tell you that the login failed. Ignore this and click “Done.”

Note that you may need to remove and re-add affected emails to Thunderbird to complete this process. It’s kind of a crapshoot.

Unfortunately, this story is accompanied by an additional problem. Several email clients, including Thunderbird and the official Outlook app, cannot maintain a connection with Microsoft’s email services. Logging in with an App Password works, but the account randomly disconnects. Microsoft is investigating the issue and explicitly mentions Thunderbird in its support post.

Source: Mozilla