page-links.php

<?php
/*
 * Create a private WordPress page with permalink as links.
 * Upload the code with the file name as page-links.php in the active themes directory.
 * Upload simple_html_dom file from here (https://sourceforge.net/projects/simplehtmldom/files/simplehtmldom/1.5/) 
 * to the same directory 
 * All done.
 * Now logged in admin, visit yoursite.com/links and you will see a list of all external links from your WordPress blog.
 * Whitelist the links and domains in the array $_allowed_links and $_allowed_domain respectively to 
 * reduce the number of links shown in the report.
 * If you don't wish to whitelabel the complete domain, add them to $_allowed_links array.
 */
?>
<ol>
<?php 
$_allowed_links = array(
  'http://imojo.in/@shabbirbhimani',
  'https://www.siteground.com/go/imtipsco',
);
$_allowed_domains = array(
  'github.com',
  'wordpress.com',
  'en.wikipedia.org',
  'policies.google.com', 
  'google.com', 
  'imtips.co',
);

$_output_domains = array();

function is_allowed_domain($url)
{
    global $_allowed_links, $_allowed_domains, $_output_domains;

    if(in_array($url, $_allowed_links)) return true;
    
    $the_domain = strtolower(parse_url($url, PHP_URL_HOST));

    if(empty($the_domain)) return true; // Hash based url

    if(in_array($the_domain, $_allowed_domains)) return true;

    if (strpos($the_domain,'www.') !== false) {
        $more_domain = substr($the_domain, 4);
    }
    else{
        $more_domain = 'www.' . $the_domain;
    }

    if(in_array($more_domain, $_allowed_domains)) return true;

    if(!in_array($the_domain, $_output_domains))
        $_output_domains[] = $the_domain;

    return false;
}
    
global $post;

include_once( get_stylesheet_directory() . '/simple_html_dom.php' );

$args = array(
    'posts_per_page'   => 9999999999,
    'offset'           => 0,
    'category'         => '',
    'category_name'    => '',
    'orderby'          => 'ID',
    'order'            => 'DESC',
    'include'          => '',
    'exclude'          => '',
    'meta_key'         => '',
    'meta_value'       => '',
    'post_type'        => 'post',
    'post_mime_type'   => '',
    'post_parent'      => '',
    'author'       => '',
    'author_name'      => '',
    'post_status'      => 'publish',
    'suppress_filters' => true 
);
$myposts = get_posts( $args );

foreach( $myposts as $post ) : setup_postdata($post); 

    //Get Post content
    $_post_content =  get_the_content();

    $html = str_get_html($_post_content);

    $links = $html->find('a');
    foreach($links as $link) {
        if (!is_allowed_domain($link->href)) {
            echo '<li><a target="_blank" href="'.get_permalink($post->ID) . '">' . get_the_title() .'</a> - '. $link->outertext . ' - ' .$link->href . '</li>';
        }
    }
endforeach;

// Only change few params for pages
$args['post_type'] = 'page';

$mypages = get_pages( $args );

foreach( $mypages as $post ) : setup_postdata($post); 

    //Get Post content
    $_post_content =  get_the_content();
    if(!empty($_post_content)) {
        $html = str_get_html($_post_content);
        $links = $html->find('a');
        foreach($links as $link) {
            if (!is_allowed_domain($link->href)) {
                echo '<li><a target="_blank" href="'.get_permalink($post->ID) . '">' . get_the_title() .'</a> - '. $link->outertext . ' - ' .$link->href . '</li>';
            }
        }
    }
endforeach;

echo '<h1>Linked Domains</h1>';
foreach($_output_domains as $domain)
{
    echo "'$domain',\r\n<br />";
}

wp_reset_postdata(); 

?>
</ol>