For performing bulk conversion of EML files to NSF format, you need to install an email migration tool that supports bulk conversion. I know a tool that can solve this problem, and that is OSTtoPSTAPP EML to NSF Converter. It provides a bundle of features that help users to perform conversion tasks easily and quickly with high accuracy. It can easily perform bulk conversion, which allows users to convert multiple files at once and process them quickly. It retains every detail of the emails authentically after the conversion and maintains the folder hierarchy. It protects the files from data loss and data corruption during the conversion.

for more information: https://www.osttopstapp.com/eml-to-nsf.html