A few months back, I was also searching for the same, then I finally found a converter that can easily convert EML files into MBOX without any data loss, and the software is named OSTtoPSTAPP EML to MBOX Converter. It preserves all my email details like its formatting, metadata, and structure, etc., in its original form after the conversion and also maintains the folder hierarchy. I thought it would not install on my Windows OS as I have an older version, but it works smoothly on my Windows Vista version. It also provides a bulk conversion facility that really helps in converting multiple files at once quickly, and it saves a lot of time. I would highly recommend using this software for safe and accurate conversion.

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