We have a medium sized environment with several discrete mail domains. The mailservers for the domains are (for historical reasons) all of a different type (HP-UX, Solaris, AIX and SGI) but are all running sendmail-8.8.8. Now in the documentation from sendmail they specificly recomend AGAINST running the mail server on a machine that is an NFS client for the user mailbox filesystem.
Stephen,
I presume that you're talking about having mbox-style mailboxes here. If you try to do this, you will run into locking problems and lose a small but measurable amount of mail -- NFS locking and cacheing just isn't up to dealing with mail delivery.
If you need to have text-based NFS-mounted client mailboxes, the only reliable option is to use a mailbox format which doesn't require locking, such as Maildir.
Nick