What is the best feature of Yahoo?

Is it possible to implement the "read at" feature in emails? If so, what's stopping service providers like Gmail and Yahoo etc. from implementing it?

• Facebook chat and Whatsapp have this feature which tells us about when the other party has seen/read the message we sent. Is it possible to implement a similar setup for emails? There's a lot of folks who say, "I haven't see your email" or sometimes they go a step forward and say "I haven't received any email from you"(while failures in sending are generally notified to the sender). If it's possible to implement this feature, why isn't being done and what are the pros and cons that you see in this?

• Answer:

  It is possible to implement "read at" feature provided the sender and receiver are from the same service provider. There is also a feature known as "read receipt" where the sender and receiver are from different service providers. Enabling this feature by default is a privacy issue and not many people want this feature hence it is not very important for service providers to implement this and spend time in other important features.