+--with-locking=LOCKTYPE (DEFAULT is dot)
+ Specify the locking mechanism when attempting to "inc" or
+ "msgchk" a local mail spool. Valid options are "dot",
+ "fcntl", "flock", and "lockf". Of the four, dot-locking
+ requires no special kernel or filesystem support, and simply
+ creates a file called "FILE.lock" to indicate that "FILE" is
+ locked.
+
+ In order to be effective, you should contact the site
+ administrator to find out what locking mechanisms other
+ mail delivery and user programs respect. The most common
+ 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.
+