When spam and virus features are turned off, the "Spam and Virus Scanning" section disappears from "Email Messages"
It has two important options that are unrelated to spam and virus scanning
"Allow mailbox users to create mail filters? and "When an over-quote user receives email"
These settings are unable to be changed when spam and virus features are disabled.
Even going to the page manually after it has been disabled, those options are missing and the page is empty.
I ran into this today when someone had a issue with over quota users, and I went to check the setting. They use a Barracuda, so they don't need the virus/spam features.