20 Servers: SuperMicro Dual Intel(R) Xeon(TM) CPU 3.20GHz Raid1
OS: FreeBSD 4.10
RAM: 4 Gb
Users: 500,000+, 5000+ simultaneously active.
Storage: Several terabytes served by NetApps.
Users Maildir Size: 500MB per user.
Dovecot version: recent 1.0-rc
Client Software: Squirrelmail Webmail client, every imap client imaginable
We run two different clusters of dovecot servers. Both clusters are highly overengineered and can handle the load easily.
- Squirrelmail/Webmail. We use 10 dovecot servers behind an alteon loadbalancer. Squirrelmail was slightly altered to connect a customer to the same imap server when possible. The squirrelmail service also consists of 10 servers + an SQL server for the customer settings.
- Direct IMAP. We use 10 dovecot servers behind an alteon loadbalancer. Customers can connect directly to their mailbox with IMAP. For POP we use different software, on a different cluster of servers. We will probably switch POP to dovecot in the future.
This first image shows the current graph of our webmail/dovecot cluster. You can see we do over 5000 simultaneous users. The week before was slightly less due to a local holiday.
The second image shows the number of connections on our direct IMAP cluster. We have over 1000 simultaneous connects on it, even though this service is still experimental and not released widely.