I am using the latest version of Thunderbird (91.5.0 32-bit) and a valid configuration of Amazon workmail. Using Thunderbird's default wizards and all the settings I can think of, I am not able to integrate Thunderbird with my email accounts. Using the default wizard, Thunderbird presents me with a dialog "Thunderbird found your account setup information on awsapps.com. Do you want to proceed and submit your credentials" Clicking the [Login] dialog brings up a control which will reads "Use the Microsoft Exchange Server or Office365 cloud service. " When I click Done, I see the dialog for the Amazon workmail client which asks me to submit my username and password where I validate my user name. Closing this dialog, however, leads to a message back in Thunderbird reading "Authentication windows was closed too early" It seems that Thunderbird is expecting some sort of validation token back from AWS which it never receives.