Remove limit 20 mappings displayed

In domain_mapping.php

/* GLerner changed 2015-06-227 was limit of 20 */
$rows = $wpdb->get_results( "SELECT * FROM {$wpdb->dmtable} ORDER BY id DESC LIMIT 0,2000" );
dm_domain_listing( $rows );

Network has 300 sites, now /wp-admin/network/settings.php?page=dm_domains_admin will show all of them.

wordpress-mu-domain-mapping development rev 1039816 ver 0.5.5.1

https://www.ads-software.com/plugins/wordpress-mu-domain-mapping/