If you are looking to import Maildir into Thunderbird efficiently?. then at this time, one of the best software are very high recommended Aryson Maildir Converter is the best tool available. It converts Maildir and Maildir++ files into MBOX format, which Thunderbird natively supports. The tool ensures a smooth transfer of emails, attachments, and folder hierarchy while avoiding data loss or duplicates. Once converted, use the ImportExportTools NG add-on in Thunderbird to import the MBOX file. Aryson’s software supports bulk migration, offers preview options, and works on both Windows and Mac systems, making it perfect for personal or enterprise-level mailbox transfers.