The default installation of elm in RH6.1 only supports flock for file
locking. flock of course does not work over NFS. If your mail spool is
NFS mounted from another machine you need to use either the dot style
locking or fcntl style.
Since Red Hat 5.2, all mail user agents use only fcntl locking. fcntl locking
works if you start rpc.lockd correctly. Otherwise please report as a bug