I know SPAM servers are a love/hate sort of thing. We love them when they capture SPAM and hate them when they capture good email.
Below are some basics stats for a one week period in March (fairly typical) to give you an indication of volumes of emails scanned. This will give you a pretty good idea as to why we use the servers and how they save us all time.
For one week (3/17-3/23/16)
Total emails: 337,196
SPAM: 247,162
% SPAM: 73%
SPAM/Staff/Day (Presume: 750 staff): 47 SPAM emails/staff/day
Virus attachments: 154 (this does not include what is caught by virus scanners on the desktop)
Annual email: 17,534,192 (not counting email sent solely within the Agency)
Annual SPAM: 12,852,424