When configuring with the mc configuration technique, you can include support for UUCP by using the MAILER(uucp) command (Section 4.2.2.2) in your mc file. With that support, you can override the use of $k ($k) with a hostname of your choosing when prefixing a string of hosts with the local hostname:

here!lady!sonya!user

 
insert local hostname here

If $U has a value, its value will be inserted. If it lacks a value, $k will be inserted.

$U can be useful when several hosts provide UUCP services. It can be defined in your DOMAIN( ) file (Section 4.2.2.3) as a single name so that all outgoing UUCP mail will appear as though it is from a common host.