There are two ways to import EML files into Thunderbird on Windows: using an automatic conversion tool or doing it manually. An automated tool can convert various files at once but in the manual method, you have to convert each file individually. Users often choose an automated tool for large files. In my own experience, I used the
Toolsbaer EML to MBOX Converter to quickly and precisely convert EML files into MBOX. During the conversion, this application keeps the original folder hierarchy and all email details, such as formatting, content, attachments and more. The tool also offers the preview option before conversion, so you can check that the files are attached correctly or not. It is compatible with every version of the Windows OS, and this tool can be operated by anyone with ot without having technical expertise.