Mac OLM to Gmail Converter

I suggest you use KDETools Mac OLM to Gmail Converter which allows users to save data in various file formats like EML, EMLX, MBOX, MSG, HTML, etc. This application maintains meta properties of email such as to, bcc, cc, subject, date, time, and etc. You can migrate particular data according to the date range using the Message Filtering option.
https://www.kdetools.com/mac/olm/gmail/