In our local network, we are sharing mailboxes via NFS- mount of /var/spool/mail from a central mail server. In Redhat 6.0, I was unable to read incoming mail with nmh/exmh and elm. Obviously, file locking (elm said 'could not lock /var/spool/mail/USER', something similar from MH's inc) didn't work with these programs. Pine and mail/mailx, on the other hand, work without problems. I guess that elm and mh (I don't know about mutt, I have never used it) use flock() system calls which are not compatible with NFS, whereas pine/mail use ioctl().
What is the mail server running?
It's running AIX 4.1 $ uname -a AIX mail 1 4 000015604600 $ However, I do not believe it's a server or general NFS-related problem, as we are using NFS heavily for different filesystems without problems.
The flock() locking is actually what NFS *does* understand. However, dot-locking has been taken out of elm and mh because of the security holes that are opened up by trying to permit both mail delivery agents and user agents the ability to write into /var/spool/mail to create dot-lock files. Probably the best short term solution for you is to recompile the src.rpm to permit dot-locking. The alternative is to run rpc.lockd on both the client and server so that fcntl locking succeeds.