Let say if you aren't able to get your email for some vacation/leave or etc. You could let the person that send you mail know. Through cPanel, you are able to do auto responder. Below is the step :
Step 1 : Login to cPanel and look for Auto Responder under Mails tab.
Step 2 : Once you clicked auto responder you will be redirected to page as following :
Click on Add Auto Responder to Setup Your Auto Responder.
Step 3 : Fill in required information as following and click "Create".