Yahoo mailbox data get corrupted due to many reason such as virus attack, system fault, unwanted deletedion, etc. To overcome from all these issue I have found Yahoo Backup Software by Mails Backup Software, it is one of the best rated aplication. This application has multiple advance features:
Simple user interface
Compatible with all version of windows
Perform bulk migration
Multiple saving option
Offers various file fromats
Free trial version
For more info visit:- https://www.mailsbackup.com/yahoo/