ALERT: Salesforce Winter ‘16 will disable Notify New Lead Owner by Default
We have researched workarounds and found that none are available. For this reason, we have deprecated the Notify New Lead Owner by Default app. While leaving the app installed should not cause any issues, it will no longer function. Therefore, we recommend uninstalling the app.
Additionally, please let Salesforce know you would like this as a feature by upvoting this idea: https://success.salesforce.com/ideaView?id=08730000000BriZAAS