corporate internal MAPI.DLL enabling these particular clients to talk to Xenix-based mail transport systems utilised this functionality. The first and almost immediately recalled version of the Microsoft Press book on using Microsoft Mail accidentally used screenshots from the Xenix backend, revealing this concealed capability of the client. Gateways Connections to other email systems were made possible by gateways to "foreign mail systems". Microsoft shipped gateways to PROFS, SNADS (Office Vision), SMTP, X.400 over X.25, Novell's Message Handling System (MHS), MCI Mail, AT&T Mail, and others. Many companies running these gateways quickly replaced them with Microsoft Exchange Server connectors once Microsoft Exchange 4.0 shipped. In particular an early part of a migration from MSMail to Exchange included replacing the Microsoft Mail for PC Networks Gateway to SMTP to the Microsoft Exchange Internet Mail Connector, later renamed to the Microsoft Exchange Internet Mail Service. Connection to UUCP-based email systems were supported indirectly, using the Microsoft Mail Gateway to SMTP client combined with a Unix system, typically running sendmail as a smarthost. SCO Unix and Interactive Unix were both recommended products for this structure, though any SMTP-UUCP smarthost-capable system would work. References Original reference 2 missing as of 2018. Replacement link: Q94178: PC WFW: Differences Between Win for Workgroups Mail & PC Mail on KnowledgeBase Archive Mail Mail Email systems