Mail Archiver X has a free demo mode which has the same functionality as the paid version. The application in demo mode can be used for 12 days. The days are counted for each day the application is used and not as calendar days.
Version 4.x is a paid update for registered users of version 3.x.
Compatibility: High Sierra (10.13) to El Capitan (10.11).
Download a FREE trial of Mail Archiver X:
Version: 4.2 beta 4