Two organizations where I've worked at (1000s of people) managed their own email infrastructure, with their own spam filter.. it ranged from 70% to 75% of incom

Two organizations where I've worked at (1000s of people) managed their own email infrastructure, with their own spam filter.. it ranged from 70% to 75% of incoming emails. Most spam emails are just a few words of plaintext, I'm surprised too the size of the stored corpus is spam in the same percentage. It seems like a few emails with medium-large attachments would outnumber the spam content which should be in the kbs/email at most.