I've a HTC Desire HD with Android 2.3.5 and I need the link to the previous Yahoo Mail update prior to Feb 2015 because it's not compatible with my device.
The application's page at Google Play Store doesn't offer the possibility to download an older version of the software. You have two possibilities:
Go to Settings > Applications > All > Yahoo Mail. Tap on it and then tap on Uninstall Updates.
Use the available email address to get in touch with the developer. Ask him about an older version of the software: firstname.lastname@example.org