This plugin allows your users to authenticate themselves on your Joomla! website with their email address (used during registration). Instead of the username, visitors simply enter the mail address of the account.
The plugin does not adapt the language files. This means that if you want the login window to say "user name or e-mail address" instead of "user name", you have to do this via Joomla's integrated language overrides.
Extension on JED: https://extensions.joomla.org/extension/authentication-e-mail-by-nxd/