This facility is useful if you are using POP, and wish for messages that are sent by users to appear to originate from the username of their POP account, rather than their username on the local machine. The name of the system-wide default .maildelivery file. This is useful for handling admin, dummy, and guest logins. Words are surrounded by white space. The first word on the line is the official name of a host.
All words following the official names are aliases for that host.
It turns out this is a major win for hosts which don't run an message transport system. This list is searched when looking for a smtp server to post mail. If a host is present, the SMTP port on that host is tried. If a net is present, the SMTP port on each host in that net is tried. This option is only available if you compiled nmh to use SendMail as your delivery agent.