function test_function( $user_meta, $user_id ) {

    $user = get_user_by( 'id', $user_id );

    if ( $user->user_email !== $user_meta['user_email'] ) {

        // Do stuff here.
        wpf_log( 'notice', $user_id, 'Email changed from ' . $user->user_email . ' to ' . $user_meta['user_email'] );

    }

    return $user_meta;

}

add_filter( 'wpf_pulled_user_meta', 'test_function', 10, 2 );