If you want to import MSG files into Thunderbird with all attachments, the best method is using  Aryson MSG Converter. This professional tool directly transfers MSG files to Thunderbird while preserving attachments, folder structure, and metadata. Unlike manual methods, which require converting MSG to EML and often lose attachments, Aryson ensures complete and secure migration. It supports batch conversion, making it perfect for handling large numbers of MSG files. Just install the tool, select MSG files or folders, choose Thunderbird as the destination, and sign in to your account. With its simple interface and advanced features like duplicate removal and date filters, it’s the most reliable and efficient way to move MSG files into Thunderbird.