In Thunderbird, I checked 'Show only subscribed folders' in the Server Settings/Advanced, then toggled Server Settings/Authentication method from the new OAuth2 to the old 'normal password' and back again.

For testing purposes, a free trial pack that converts the first 25 items from the Thunderbird mbox folder to Office 365 is also available. Update: the problem seems to have been with Office365, apparently just barely still compatible with IMAP folders. Next, click on the OK button to migrate Thunderbird email to Office 365 or Microsoft 365. Up to version 11 of Windows and Outlook are supported. In the Create New folder dialogue box, set a name for the new folder. Without any limitations, it can convert MBOX files of any size. Give users two options for choosing a Thunderbird MBOX file: (1) Auto-load all Thunderbird files from their precise locations, and (2) Manually select Mbox files. Its straightforward user interface makes it simple to use and understand. View other versions Provider for Exchange ActiveSync Add sync support for Exchange ActiveSync (EAS v2.5 & v14. Rated 5 out of 5 stars (156) 50,917 users Download Now Works with Thunderbird 91.0 - 102. Key Features of Thunderbird to Outlook 365 Converter Tool Export Thunderbird to Office 365 Single or bulk at once. Allows you to use your Exchange and Office365 email account with Thunderbird using Outlook Web Access (OWA). It contains several advanced features, which is why it has become the most well-liked software product. One of the better solutions for converting thunderbird data is the Softaken Thunderbird to Office 365 Converter program. This tool will convert your Thunderbird data to Outlook 365 immediately and without any problems.

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