"Return-Receipt-To" header should send a reply if a message is delivered properly
Google Apps ended their free level of service. In April 2014, Microsoft ended the Outlook Custom Domain service (without grandfathering # of accounts per domain!). Apparently Zoho.com offers 5 users for free email.
Terminology: POP3 "global mailbox" - e.g. Exchange POP3 connector. All emails for domain in one POP3 box, server picks up and distributes. I think this is the same as a catch-all.