+.PP
+If
+.I users
+are given, then
+.B msgchk
+will only check the default system mail drops.
+Otherwise,
+.B msgchk
+will evaluate the environment variable
+.I MAILDROP
+and profile component
+.I MailDrop
+(in this order) first and, if they are set and non-empty,
+checks that mail drop instead of the system default mail drop.