I have been approached about possibly setting up an email server to host anywhere up to 10,000 accounts, with a possibility of moving up to 40,000 accounts. All of these accounts would be provided to our clients on a temporary basis (3-6 months), and would only have like 2MB storage alloted to each of them. We are looking to have this be used primarily as a POP server, though there is interest in having clients access their accounts through the webmail interface.
I am having trouble finding any documentation from MS stating what kind of hardware/software would be required for an install of this size. I would assume that these kinds of numbers would require a license for Exchange Enterprise Edition, but please let me know if I am incorrect there. I would also assume that it would only make sense to have at least a front and back end server configuration to scan for spam and viruses and such as well as to separate the processing load for such activities.
Basically, I am in the basic information gathering phase of this project, and would love any links or opinions that you might have on this topic. Also, if you know of another email server platform (something Windows based preferably) that you think would work better here, I would like to know it also. Thanks!