I wrote:

> However, I'm using an NFS-mounted mailspool between hosts
> running:
>
>        NetBSD, SunOS, Solaris, Linux, AIX, Ultrix


Oops, Ross Harvey reminds me that I edited out that I use using
bellmail locking (aka dot-locking). This has worked very happily for
me since I Andy Linton (with kibzing from me) hacked in dot-locking
*and* flock/lockf() into binmail for the UIUC sendmail kit, nearly a
decade ago.

The kind of thing I have in mind is an /etc/mail.local.conf, to
override the compiled-in choice of lockstyles and maildrop...