If you want to move MSG files to Mozilla Thunderbird on Mac, you first need to convert them into a compatible format like MBOX or EML, since Thunderbird does not support MSG files directly. A reliable solution is using Aryson MSG Converter, which simplifies the process.

Install and launch the tool on your Mac, then add your MSG files or folders. Preview the emails and choose MBOX or EML as the output format. Select a destination path and start the conversion. Once done, open Thunderbird and import the converted files using the ImportExportTools add-on.

This method ensures all email data, including attachments and metadata, remains intact while making MSG files fully accessible in Thunderbird without Outlook dependency.

Read Also: https://www.aryson.in/blog/import-msg-files-to-thunderbird/