This service has been clearly aimed at large (or complicated) organizations that might be managing multiple domains. It can do clever tricks such as rewriting email addresses and handling subdomains that may not have been specifically configured. Administrators can be created with limited sets of responsibilities.
IntY's MailDefender manages to squeeze quite a lot of mail filters and controls into an attractive and uncomplicated interface. We might have preferred the default first screen to be the useful quarantine summary (giving customer-wide mail totals), rather than the actual quarantining itself, but this was just a minor quibble.