Source

File: wp-includes/pluggable.php

function wp_new_user_notification( $user_id, $deprecated = null, $notify = '' ) {
		if ( null !== $deprecated ) {
			_deprecated_argument( __FUNCTION__, '4.3.1' );
		}

		// Accepts only 'user', 'admin' , 'both' or default '' as $notify.
		if ( ! in_array( $notify, array( 'user', 'admin', 'both', '' ), true ) ) {
			return;
		}

		$user = get_userdata( $user_id );

		// The blogname option is escaped with esc_html() on the way into the database in sanitize_option().
		// We want to reverse this for the plain text arena of emails.
		$blogname = wp_specialchars_decode( get_option( 'blogname' ), ENT_QUOTES );

		if ( 'user' !== $notify ) {
			$switched_locale = switch_to_locale( get_locale() );

			/* translators: %s: Site title. */
			$message = sprintf( __( 'New user registration on your site %s:' ), $blogname ) . "\r\n\r\n";
			/* translators: %s: User login. */
			$message .= sprintf( __( 'Username: %s' ), $user->user_login ) . "\r\n\r\n";
			/* translators: %s: User email address. */
			$message .= sprintf( __( 'Email: %s' ), $user->user_email ) . "\r\n";

			$wp_new_user_notification_email_admin = array(
				'to'      => get_option( 'admin_email' ),
				/* translators: New user registration notification email subject. %s: Site title. */
				'subject' => __( '[%s] New User Registration' ),
				'message' => $message,
				'headers' => '',
			);

			/**
			 * Filters the contents of the new user notification email sent to the site admin.
			 *
			 * @since 4.9.0
			 *
			 * @param array   $wp_new_user_notification_email_admin {
			 *     Used to build wp_mail().
			 *
			 *     @type string $to      The intended recipient - site admin email address.
			 *     @type string $subject The subject of the email.
			 *     @type string $message The body of the email.
			 *     @type string $headers The headers of the email.
			 * }
			 * @param WP_User $user     User object for new user.
			 * @param string  $blogname The site title.
			 */
			$wp_new_user_notification_email_admin = apply_filters( 'wp_new_user_notification_email_admin', $wp_new_user_notification_email_admin, $user, $blogname );

			wp_mail(
				$wp_new_user_notification_email_admin['to'],
				wp_specialchars_decode( sprintf( $wp_new_user_notification_email_admin['subject'], $blogname ) ),
				$wp_new_user_notification_email_admin['message'],
				$wp_new_user_notification_email_admin['headers']
			);

			if ( $switched_locale ) {
				restore_previous_locale();
			}
		}

		// `$deprecated` was pre-4.3 `$plaintext_pass`. An empty `$plaintext_pass` didn't sent a user notification.
		if ( 'admin' === $notify || ( empty( $deprecated ) && empty( $notify ) ) ) {
			return;
		}

		$key = get_password_reset_key( $user );
		if ( is_wp_error( $key ) ) {
			return;
		}

		$switched_locale = switch_to_locale( get_user_locale( $user ) );

		/* translators: %s: User login. */
		$message  = sprintf( __( 'Username: %s' ), $user->user_login ) . "\r\n\r\n";
		$message .= __( 'To set your password, visit the following address:' ) . "\r\n\r\n";
		$message .= network_site_url( "wp-login.php?action=rp&key=$key&login=" . rawurlencode( $user->user_login ), 'login' ) . "\r\n\r\n";

		$message .= wp_login_url() . "\r\n";

		$wp_new_user_notification_email = array(
			'to'      => $user->user_email,
			/* translators: Login details notification email subject. %s: Site title. */
			'subject' => __( '[%s] Login Details' ),
			'message' => $message,
			'headers' => '',
		);

		/**
		 * Filters the contents of the new user notification email sent to the new user.
		 *
		 * @since 4.9.0
		 *
		 * @param array   $wp_new_user_notification_email {
		 *     Used to build wp_mail().
		 *
		 *     @type string $to      The intended recipient - New user email address.
		 *     @type string $subject The subject of the email.
		 *     @type string $message The body of the email.
		 *     @type string $headers The headers of the email.
		 * }
		 * @param WP_User $user     User object for new user.
		 * @param string  $blogname The site title.
		 */
		$wp_new_user_notification_email = apply_filters( 'wp_new_user_notification_email', $wp_new_user_notification_email, $user, $blogname );

		wp_mail(
			$wp_new_user_notification_email['to'],
			wp_specialchars_decode( sprintf( $wp_new_user_notification_email['subject'], $blogname ) ),
			$wp_new_user_notification_email['message'],
			$wp_new_user_notification_email['headers']
		);

		if ( $switched_locale ) {
			restore_previous_locale();
		}
	}