NFS Locking Question

[James]

On 25/05/2021 16:46, Zane Zak wrote:
> We have a single exim server that delivers mail to mbox files in /var/mail. We have a separate
> server running dovecot that reads mail from these mbox files.
...
> Is there a configuration change that needs to be made on the dovecot

I don't know about the NFS problem but change your configuration to use 
LMTP delivery.

https://wiki.dovecot.org/LMTP/Exim

Plus there are plenty of reasons to not use mbox.