How to Enable Less Secure Apps in Yandex Mail

Step 1: Login Yandex Mail Account

Step 2: Go to 'Account Management' (Right Side on Top)

Step 3: Create 'App Password' for accessing Third Party Tool

Step 4: Use this password for Login in Regain Yandex Mail Backup Software

Enable IMAP Setting as well if not.

Otherwise Regain Yandex Mail Backup software not able to access your Yandex emails. Here is the screenshots, where you can change setting.