Make sure you are running the latest version of Thunderbird (version 91.3 as of this writing).

To switch Thunderbird to OAuth2 authentication: To keep Thunderbird working, a minor setting needs to be changed in your Thunderbird account settings.

If you use Thunderbird to access your Rutgers Connect email account, then it may be setup with the old authentication settings that Microsoft will be retiring in the coming months. Rutgers is activating this change early so we can deal with any problems that arise before Microsoft makes the change irreversible. In an effort to enhance the security of the mail system, Microsoft, like most major e-mail providers, is making a change. Once it is toggled to “true” then QUIT Thunderbird entirely, wait fifteen seconds, then launch Thunderbird again.See the OIT documentation for instructions on how to setup a new Thunderbird account with OAuth2 settings. Click on the TOGGLE icon (1st icon on the right hand side) so it toggles to TRUE. In the search bar at the top search for “6” without the quotes. In the General section (this should be where you are already), scroll all the way down to the bottom and click CONFIG EDITOR This will take you into the settings menu. In the main Thunderbird window click on the cog wheel in the bottom left hand corner OR click on File -> Settings. Sometime at the end of December a change was made either in Thunderbird or Microsoft which requires you to disable IPv6 in Thunderbird. Thunderbird IMAP says 'User is authenticated but not connected' message

If IMAP is enabled for your mailbox you can configure the mail client to use the following settings. We will look at the request and make the determination as to whether or not there is sufficient reason to enable IMAP for your mailbox. Since IMAP is disabled by default for all user mailboxes you will need to complete a HelpCenter ticket and request IMAP be enabled for your mailbox. For Linux users we recommend Mozilla Thunderbird be used.

Outlook 365 and Outlook for Mac, which can be downloaded through the interface, are recommended if a desktop e-mail application is needed. Outlook Web App () is the preferred method. We highly recommend using Microsoft Outlook when accessing e-mail.

Smtp office 365 thunderbird