The MailArchiver plugin for WordPress is vulnerable to Stored Cross-Site Scripting via admin settings in all versions up to, and including, 4.4.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level permissions and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This only affects multi-site installations and installations where unfiltered_html has been disabled.
https://plugins.trac.wordpress.org/browser/mailarchiver/trunk/includes/system/class-form.php#L92
https://github.com/Pierre-Lannoy/wp-mailarchiver/commit/946c1a700bbecc6080a427fd428de800334af824