[CentOS] e-mail serving

I am  going to try an experiment with e-mail aggregation where I expect to
receive over 1 million e-mails a day from public lists.

Can anyone shed some light on hard disk space (to retain this e-mail for
long periods) and system specs to be able to handle the load?

I am looking to buy a low end box, but that can hold lots of RAM and
accomodate a fair number of HD's to store the e-mail while I try my
experiments.

Can anyone provide some realistic specs while maintaining a small budget?

-Jason
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