Simply because of lack of one simple restriction.
We allow the mails that are coming in to leave our network. This opens us to the threat of being blacklisted as a spam site.

The worldsoft-atmail system does not allow forwardiing of incoming emails to external sites.

This Q&A was found on Worldsoft Atmail hosted mail service : https://worldsoft-atmail.com/modules/smartfaq/faq.php?location_id=45&faqid=27