I've posted this to the Wiki as requested.

Servers: 2 SuperMicro single-Xeon (dual-capable) 2.8, 1gb RAM,
mirrored SATA boot Storage: 1 SuperMicro dual-Zeon 2.8, 2gb RAM, 600GB RAID5 SATA shared
via NFS over GigE OS: RHEL 4 Users: 10,000 mostly POP users, SquirrelMail IMAP Auth: MySQL Maildir size: daily averages about 50gb Dovecot version: 1.0 beta 5 Client Software: squirrelmail, outlook, outlook express, thunderbird,
eudora, Apple Mail, Claris Emailer, and other odd clients too
numerous to mention

This system is intentionally over-engineered, to replace the single
server Courier-IMAP system that it replaced. Load on each Dovecot/ SquirrelMail server is very low and allows for a lot of growth.

Our incoming MTA is Exim, on another pair of SuperMicro machines
writing to the same NFS over GigE.

-- Roger J. Weeks Systems & Network Administrator Mendocino Community Network