I've briefly looked at Zimbra in the past but have had concerns about it's ability to scale to large numbers of users. After recently reading that Comcast has chosen to use Zimbra, I thought I'd revisit to see what's changed. I see that RHCS is supported now and that's interesting. I've not been able to locate any statistics that can help determine number of machines/number of accounts though. We currently have --
1 - 2x sendmail mail relay machines running RBLs, Mailscanner for A/V, attachment stripping, phishing detection
2 - 4x postfix machines running postfix/SA for per-user spam scanning and final delivery.
3 - 4x Courier-IMAP for pop/imap access
4 - 5x openldap servers for user account information. 1 master, 4 replicas
5 - 1x Squirrelmail for webmail.
6 - 1x Netapp for mail storage.
We currently have approximately 40,000 users with a total of 850GB of mail and about a dozen domains. Most users have <100M of mail about a dozen are in the 1-3GB range. In the last week we processed just at 17,000,000 messages of which, about 1,000,000 made it to users mailboxes. ~75% were deleted at the mail relay level and ~25% were deleted by spamassassin at the MTA level.
Since Zimbra utilizes many of the same programs and the architectural layout is nearly identical, I expect that the hardware requirements would be pretty much the same. Is that the case? What are other large installations utilizing? How's it working? Pointers on where to look would be ok too.
I expect that Zimbra would replace 2-5 above.