Google GMail which was one of the first to use Label to associate your emails from different individuals or originators. Now Google has taken Labeling another step forward with the introduction of nested Labeling. With the new nested labeling feature, you can now sort your mails according to sub-labels or child-labels.You can create complex hierarchies of labels if that's the way you like to organize your mail, and you can expand/collapse labels to save space. You'll always be able to tell whether a given label contains unread messages in its collapsed child labels by looking at whether it's bold or not.