How to avoid duplication of accounts/lead/contacts?

How to avoid duplication of accounts/lead/contacts?

Hi, I´m using Zoho CRM professinal edition and I want to know how can I prevent the duplication of data in my CRM.

For example, is any way to detect that am creating an contact with an email that already exist in a lead? 

Example:
Existing Lead
Name: John Smith
Email: js@gmail.com


¨New¨ contact
Name: John
Email: js@gmail.com


I want to know if Zoho can detect this ¨duplicate¨ data?