reason not to use dot-locking is if the mail spool directory
is not world- or user-writeable, and thus a lock file cannot
be created.
+
+--with-lockdir=DIR
+ If you have defined "dot" locking, then the default is to
+ place the lock files in the same directory as the file that
+ is to be locked. Alternately, if you use this option, you can
+ specify that all lock files go in the specified directory.
+ Don't define this unless you know you need it.
+
+ This option is only relevant if "dot" locking is used.
+ In the other cases, it is ignored.