You can easily Save Yandex email files using MacUncle Yandex Mail Backup Tool. The tool supports Mac OS Machines.
Start MacUncle Yandex Backup on Mac OS.
Enter Gmail Account Credentials - Yandex Account Address & Password on the panel.
Select the folder and choose the respective format from PST, EML, MBOX, HTML, MHT, CSV, OLM, Thunderbird, IMAP, etc.
Advanced Filter option to backup Yandex Mail of specific date & Export selective folders. Then, Click Start Backup to start the Yandex Backup process.