Use of NetApp filer technology to act as the storage portion of large scale e-mail installations is a relatively common application of our products. Almost "routine" in fact! :-)
A very good technical paper has been written by one of our customers on this subject, which can be perused at:
http://www.earthlink.com/about/papers/mailarch.html
A similar paper describing the net news application of filers is also available from:
http://www.earthlink.com/about/papers/scalenews.html
A recently published article on the subject of "Hosting E-Mail for Heavyweights", involving our storage solutions can be viewed at:
http://www.internetworld.com/print/1998/10/12/infrastructure/19981012-hostin... tml
And finally, one of our own papers on the subject of e-mail performance benchmarking is available from:
http://www.netapp.com/technology/level3/3022.html
All just FYI...
Keith