We're estimating an eventual 3000+ email boxes over several domains running on a rack server with a 100Mbps internet connection. Probably 30-50MB mailbox limit, and supporting secure connections (though will won't be used by clients often).
Any ideas on how to estimate processor, memory and hard disk space? We need to keep costs as low as possible.
We may purchase a dual CPU motherboard but only one CPU, then add another later if necessary - though it'll be hard to get exactly the same model etc.