Hi shekala,
It's not currently possible to search for tasks or notes that were added via email, sorry. When you select a task to view its details, you will see Sent from: Emailed in if the task was added by email. However, there's currently no way to search for this.

If this is something you'd like to see in the future, you may want to vote for this in our Ideas forum here.

Thanks for your feedback.