An email Feedback Loop is a mechanism where an ISP lets you know when subscribers mark your email spam. An ISP can block your IP due to increased spam complaints. Instead, know your unhappy subscribers, filter your emailing lists and stay clean.
Refer : http://en.wikipedia.org/wiki/Feedback_Loop_(email)

How does this work in Zoho

1. You send an email to a Zoho user on behalf of your customer/user
2. Recipient marks your email as spam
3. You receive a notification with a email report in ARF(Abuse Reporting Format)

Benefits of Email Feedback Loop

An email Feedback Loop helps you stay clean by maintaining your IP reputation, improve email deliverability, decrease spam complaint rate and get rid of unhappy subscribers. Unhappy subscribers can be the cause of increased complaint rates due to mistaken sign ups or a long delay between sign up and first email. Hence, the Feedback Loop helps organization's improvise on overall quality of user subscription.