Converting MBOX files to EML in bulk saves time when you have email archives from Thunderbird, Apple Mail or other MBOX supported email clients. Instead of exporting each mailbox separately, select multiple MBOX files and convert them together.
My suggestion is to use DataVare MBOX to EML Converter Expert, which supports bulk conversion and lets you select specific MBOX files for export. You can choose a local destination folder for the resulting EML files. The software also claims to preserve email properties, message text and folder hierarchy. Keep in mind that only healthy MBOX files are supported.
Before converting your entire archive, check a few output EML messages to confirm they meet your requirements.