First of all the per cent depends on how much legit mail you get. Notice near-constant stream of spam, but different ratios:
Tuesday 10/16/2007 GARBAGE STOPPED: 3997006 (76 % of all mail (5220524)) 1588777 (30 %) spam and other junk detected and rejected 2408229 (46 %) no recipients given or connection denied Saturday 10/13/2007 GARBAGE STOPPED: 3905965 (92 % of all mail (4236042)) 1768719 (41 %) spam and other junk detected and rejected 2137246 (50 %) no recipients given or connection denied Additionally, we count all of our mail including what our users send to each other. I could make that 92% higher by counting only mail from "outside" however I choose to define that. Secondly, this is a good point:
These figures are probably including DSNs to fake mail addresses
See the "no recipients given"? Almost all of that is bounces of undeliverable spam to nonexistent sender addresses. I want to to count it for management as smtp traffic we have to deal with, but it is also true that it's not the same as the other spam. There are so many ways to count spam. Joseph Brennan Columbia University Information Technology
