I have a special requirement to implement mail server(cyrus imap) with pam_mysql and mysql authentication. I plan to handle 200K to 350K accounts(mailboxes) with 1Gb mail quota and i am expecting 5% of users will access the server simultaneously.
Following are the statistics about the mail quota using by users.
estimated storage capacity 160TB

I have some clarification from the above mentioned scenario

1. Is there any limitation for user accounts(mailboxes), user quota in cyrus imap?
2. Is single cyrus imap will handle these all?
3. What is the minimum hardware(cpu, memory and storage) requirement for this scenario?
4. Here we are using HP servers(DL380, DL580). which is most preferable?
5. Which operating system is most suitable for this scenario(here i am using RHEL5.2)?
6. How yahoo, gmail handling this unlimited user quota and simultaneous access?

I really appreciate your valuable comments in this regards.

Thanks

Any suggestion highly appreciate

I had cyrus running with about 1.8M user accounts although the active ones are way below, although the quota is just 10MB, the main limitation is the file system you cannot use ext3 (because of a limitation on the number of files in a directory) ext4 removes that limitation but i used reiserfs as ext4 was not released at the time. There are other limits you will need to adjust on the OS to.

yahoo and gmail etc use clusters to handle that not single nodes. You can get cyrus to work in a clustered setup (murder) or you can use a SAN/NAS or use imap replication to distribute the load.

Other deployments

http://cyrusimap.web.cmu.edu/twiki/b...usInstallation
http://cyrusimap.web.cmu.edu/twiki/b...eCyrusHardware