In an ideal world (from the Internet perspective), all hosts have records in the Domain Name Service (DNS) and will send mail with fully qualified domain names.
If you happen to talk via UUCP to such a site, you can force mail to go through the point-to-point UUCP connection rather than through your default mailer by essentially ``undomainizing'' their hostname through the uucpxtable.
To force UUCP delivery to sesame.com, you would put the following in your uucpxtable:
The result is that sendmail will then determine (via UUCPNODES in the sendmail.m4 file) that you are directly connected to the remote system and will queue the mail for delivery with UUCP.
Thu Mar 7 23:22:06 EST 1996