+The macros
+.b $w ,
+.b $j ,
+and
+.b $m
+are set to the identity of this host.
+.i Sendmail
+tries to find the fully qualified name of the host
+if at all possible;
+it does this by calling
+.i gethostname (2)
+to get the current hostname
+and then passing that to
+.i gethostbyname (3)
+which is supposed to return the canonical version of that host name.\**
+.(f
+\**For example, on some systems
+.i gethostname
+might return
+.q foo
+which would be mapped to
+.q foo.bar.com
+by
+.i gethostbyname .
+.)f
+Assuming this is successful,
+.b $j
+is set to the fully qualified name
+and
+.b $m
+is set to the domain part of the name
+(everything after the first dot).
+The
+.b $w
+macro is set to the first word
+(everything before the first dot)
+if you have a level 5 or higher configuration file;
+otherwise, it is set to the same value as
+.b $j .
+If the canonification is not successful,
+it is imperative that the config file set
+.b $j
+to the fully qualified domain name\**.
+.(f
+\**Older versions of sendmail didn't pre-define
+.b $j
+at all, so up until 8.6,
+config files
+.i always
+had to define
+.b $j .
+.)f
+.pp