[Dovecot] Multiple Dovecot instances over single mail store

[Zohan]

Hi,

I need to run two Dovecot instances with totally different
authentication configs: first - passwordless, based on client SSL
certificate; and second - regular password based (LDAP, passwd etc.).
(As far as I know this cannot be achieved with single Dovecot instance;
if I'm mistaken, please correct me). My intention is to give clients
dual access to their mailboxes: some do own a SSL cert, others do not.

I want to know whether it is possible at all. If possible, how do we
implement proper concurrent access (locking, etc.) between the two
instances to a single maildir-based store? I guess this should be
possible since I know Dovecot can operate NFS-backed mail stores, e.g.
in a load-balancing cluster setup.

Second, is it OK to run the second instance in the same OS (we use
Linux)? or chroot'ed or even virtualized solution will work better?

Thank you!
Zohan