Spam is considered a spam if the grading system hits a certain value (i.e. 3, 5, 10) - which in turn depends on that particular customer's settings.
Customers can choose to be set low, high or even off.
The basic settings are in the Aspam area of the SpamControl page.

Each account, as well as each Domain, can also choose to implement SPF on the incoming emails. The system will send back a 550 error message that includes a link for people to click on (which will be read by the person if it's in fact a person, not a spambot.)

BarryZ
Reading PA