Hi p@rick and thanks for the response.
Michael,
- Michael Wessel <michael@think-for-yourself.org>:
I'm currently (re-)planning my email setup and have been doing some research. I have done some searches and read several threads in the areas of my questions here. While there are some that come close I haven't yet been able to get all my questions answered.
I currently run a postfix, dovecot & roundcube setup and have about 2000 active accounts. I have a separate SMTP server for outbound mail and auth is done against a separate LDAP server. In front of the POP/IMAP server I have another SMTP (4 in parallel actually) server that receives and filters inbound mail through a company specific, proprietary filter before the mail hits the POP/IMAP server. LDAP & SMTP servers are ESXi VMs. Do people use 'real' mail clients to connect and IDLE too? Yes, though not sure of the percentage. Most will likely use webmail, some will use POP and some will use IMAP with "real clients". Right now my guess would be about 20% IMAP with Outlook, Thunderbird and such, 10% POP and the rest webmail.
So right now both dovecot and roundcube run on the same box which is a Dell PE2950 with dual quad-core Xeon, 16GB RAM and 6 1TB disks in RAID 6, so only local storage using maildir. So far it's been holding up fine, but it's beginning to show signs of overload now. I also expect an increase in users over the next few months up to somewhere between 10 - 20,000 mail boxes. Hence the re-planning.
My first priority in redesigning my setup is reliability. I definitely need something fail-save and as close to always on as possible. Next is performance. And while the budget is of course limited for the moment I'm setting that aside and will worry about that when the time comes.
Now here is my question(s):
In order to support up to 20,000 mailboxes (distributed over several times-zones so they won't all be used at the same time) with a very reliable service with good performance, what do I actually need?
Do I need(ul) SAN or is it just a "would be nice to have"? If yes, why and what would be appropriate for my needs? Or will a setup with a few more servers like the ones I already have, using something like DRBD and distributing services (imap, http, spamd etc) onto different boxes do? Will the server enforce quota? Yes, default quota is 200MB right now, some have larger quotas and a few of those hit several GB.
What will be the average mailbox size? Since the quota is probably going to go up some I'd guess around 400MB on average.
Do people share content e.g. mailings with attachments that go out to all recipients? No, only on a limited basis (like cc'ing maybe 15 or so people but even
On 6/23/2012 3:25 AM, Patrick Ben Koetter wrote: that's rare) There will be somewhat large attachments involved (20-30MB) but that's mostly between individual users and users outside my system.
What might be the maximum number of clients using the server at one time?
Hard to say with the data at hand. I have a caching IMAP proxy for webmail and that has so far recorded 50 as the highest concurrent connections. So adding IMAP users to that and then extrapolating this to 20000 total boxes I'd say 4-500.
Will all users use the same client product e.g. roundcube?
No, they have their choice of any POP3/IMAP client or webmail
What's your backup strategy? What do you use to backup mailboxes?
I was afraid someone was going to ask that question... there isn't one (it hurts just writing that!) The only "backup" currently in place is redundancy on the hardware-side plus limited (i.e. only parts of the mail store) to disk backup. The VMs are easily replaced, but if my maildir goes up in smoke tomorrow then I will probably follow shortly after! So that's definitely part of what I'm working out here. Wanted to nail down the general approach first though before looking at that.
p@rick