[Dovecot] advices for a new installation

[Surviet Amine]

hello everyone,
first of all, please forgive my bad english skill, I live in France.
On our "old" Dovecot 1.x architecture, we have NFS shares between the front
servers (MTA, IMAP...) and mail storage server.
I've read some wiki2 pages that present the new director and imap proxy.
But I'm still don't see things clearly, so I post here to have your advices
to set-up a new mail architecture.

The hardware we have :
- 24x hard drives in a SAS bay
- this bay is directly attached via SAS to a server that I'll call : mail
storage server
- 2 others servers run ProxMox Virtual Environment

The PVE will help us to get many virtual servers :
- MX : "mail in" servers
- IMAP/POP : our hosted clients services
These clients may come from webmail (RoundCube) and others clients
(Outlook, Thunderbird, mobile clients...)
- RoundCube webmail
- MySQL server (hosts in databases accounts and settings for Postfix,
Dovecot and RoundCube)
- maybe antivirus and antispam servers

I've read several threads about NFS and IMAP issues.
So I decided to not keeping it.
In this scenario, I've tried for the mail receiving part :
- front-end (postfix lmtp-client) to mail storage server (lmtp server)
that seems to runs fine, now i'll must try to add antispam and antivirus
scans

Now, for the IMAP part, could you, please tell me, if it is better to :
- have several IMAP frontend servers that proxy to the mail storage server
or
- still keeps NFS between the mail storage server and the frontends Dovecot
?

On our Dovecot 1.x webmail use imapproxy.
I've read that others proxies exist.
We have used for a limited time Perdition.
What is the differences between imapproxy, Perdition, nginx imap proxy and
Dovecot proxy ?

Thanks for sharing your experience of "large mail service" that are solid
enought to be scaled.