Why does the MTA take so much power?
The reason I ask is I remember when I worked for the (then) largest ISP in the northwest in late 2000, they had 3 Sun servers for email doing round robin, running SunOS I believe, and I think they were only like 80 MHz with 512 MB RAM, but they handled email for 50,000 customers and only got slow when we got hit by massive spam storms (like millions at a time).
Now granted, I realize that a) this was years ago and spam has grown exponentially since then and b) they were not running a collaboration suite, just basic email and mailing list services, but still, 50,000 customers on servers that were very old even by 2000 standards.
I also remember around 2002 working at another ISP and we bought a smallish ISP out. We moved their mail server into our office and that little whitebox by itself was supporting probably 5,000 customers, and it was an old piece of crap.
My dedicated Zimbra NE server here at work supports 49 users, and it's got 4 GB RAM and a quad-core 64-bit CPU AND STILL runs quite slow at times... Amazing..