[exim] Hardware for emailserver for 500 to 1000 Users

Hi,
sorry for applying not a exclusive exim question but I hope I find the
necessary competence.

What (PC) hardware (I/O performance, throughput) is to be recommended
for a email server with exim4, courier imap, sqwebmail, postgresql for
authentication of the virtual users, etc.
for about 500 - 1000 users?

Many thanks
Rainer Sigl

-- 
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Rainer Sigl,                      | email: sigl@???
MPI f. extraterrestrische Physik, | phone: +49 (89) 30000-3557
Postfach 1312,                    | fax:   +49 (89) 30000-3569
D-85741 Garching, Germany         | web:   http://www.mpe.mpg.de/~sigl/