|The UUCP relay for unclassified hosts
$Y holds as its
value the name of the host that will handle all UUCP mail that was
not otherwise handled by class $=V,
$=W, or $=X. See Section 4.6.6 for a discussion of UUCP relays in general,
and how this macro relates to $V,
$W, and $X macros.