[Dovecot] proxy performance

[Vincent Fox]

Can anyone speak to experience using Dovecot proxy to frontend for multiple
back-end servers in a "large" environment?

We have 50,000+ mailboxes spread across 10 POP/IMAP servers. We'd like to
be able to put in a front-end setup on our load-balancer of 4 dual-CPU Sun
systems. I am a bit concerned about performance issues although from what I
have read the proxy can be set not to fork, which improves performance a
lot. Still concerned about whether SSL loading will be an issue.

We'd like to use LDAP to look up the reference to which mail-store a user
is on. I see that the Wiki refers to SQL. The mailing list indicates
passwd-file also works. Not clear about LDAP.