I'm a Microsoft Exchange administrator for a company with 8,000 or so users.:) I'm not going to dis qmail or any of the other solutions proposed because honestly I don't know enough about them to form an opinion. I've been working to expand my knowledge of other e-mail platforms but I'm a work in progress OK?
In regards to Exchange's scalability we're running Compaq Proliant 6500s with 512 MB of ram and Quad Pro 200 Mhz processors. Currently an average server holds approximately 1,600 users. CPU utilization hovers around 20-25%. For a while one box was running with approximately 2,500 users on it, but we spread out the users for load balancing.
Is Exchange THE enterprise solution? No, there are numerous products which could be used as you've all stated. But, Exchange is scalable enough to support a large number of users.
One drawback to Exchange is they way the information store is currently handled. As a single database it can get pretty large and so most Exchange server loading is restricted by the size of the information store rather than by the number of users. That limit tends to be at around 30GB because larger information stores require too high of a restore time in the event of disaster recovery for most organizations. So, you can take the average size you wish a users mailbox to be and divide that by 30GB to arrive at a rule of thumb number of users. (The next version of Exchange (is that 3.0) will address the IS size issue natively)
Using CommVault, one could probably triple the size of IS and thus increase the number of users per box.
I will admit we use the Outlook Client which connects via the Microsoft Exchange service, rather than POP3 or IMAP4. I know of no tool to load test an Exchange server running as an IMAP4 server so these numbers are not necessarily accurate for that.
Probably the biggest drawback for this group is the lack of an Outlook Unix client (not that I would imagine you all would be clamoring to use it). Microsoft has indicated they are working on one... but I'm not holding my breath.
There are also a variety of helpful resources and links for Exchange. I know of few questions one couldn't work out in an Exchange implementation with a little help from one of the Microsoft Exchange mailing lists.
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I'm probably going to regret saying this but...
:) I'm not going to dis qmail or any of the other solutions proposed because honestly I don't know enough about them to form an opinion. I've been working to expand my knowledge of other e-mail platforms but I'm a work in progress OK?
I'm a Microsoft Exchange administrator for a company with 8,000 or so users.
In regards to Exchange's scalability we're running Compaq Proliant 6500s with 512 MB of ram and Quad Pro 200 Mhz processors. Currently an average server holds approximately 1,600 users. CPU utilization hovers around 20-25%. For a while one box was running with approximately 2,500 users on it, but we spread out the users for load balancing.
Is Exchange THE enterprise solution? No, there are numerous products which could be used as you've all stated. But, Exchange is scalable enough to support a large number of users.
One drawback to Exchange is they way the information store is currently handled. As a single database it can get pretty large and so most Exchange server loading is restricted by the size of the information store rather than by the number of users. That limit tends to be at around 30GB because larger information stores require too high of a restore time in the event of disaster recovery for most organizations. So, you can take the average size you wish a users mailbox to be and divide that by 30GB to arrive at a rule of thumb number of users. (The next version of Exchange (is that 3.0) will address the IS size issue natively)
Using CommVault, one could probably triple the size of IS and thus increase the number of users per box.
I will admit we use the Outlook Client which connects via the Microsoft Exchange service, rather than POP3 or IMAP4. I know of no tool to load test an Exchange server running as an IMAP4 server so these numbers are not necessarily accurate for that.
Probably the biggest drawback for this group is the lack of an Outlook Unix client (not that I would imagine you all would be clamoring to use it). Microsoft has indicated they are working on one... but I'm not holding my breath.
There are also a variety of helpful resources and links for Exchange. I know of few questions one couldn't work out in an Exchange implementation with a little help from one of the Microsoft Exchange mailing lists.
Whatever you decide to go with, I wish you luck.