A new feature in Moodle 2.7 allows the administrator to enable users to login by both their username and their registered email easily…which is to say, probably a feature that Moodlers across the globe will embrace as a way to cut down on “I forgot my username” tech tickets.
The feature can be enabled on a 2.7 site at yourmoodlesite.com/admin/settings.php?section=manageauths in Common Settings.
Check out the other great new features for Moodle 2.7 here: http://docs.moodle.org/27/en/New_features