How to prevent emails from users on the same domain being marked as {Spam?}?

[Meeven]

On a cPanel server running MailScanner for the last several years, for some strange reason, emails from all users on the domain to each other are being suddenly marked as spam.

I checked spam.scanning.rules at /usr/mailscanner/etc/rules/ and found an entry that marks incoming emails to this domain to be scanned:
To: *@domain.com yes

The solution seems to be to define a ruleset at /usr/mailscanner/etc/rules/scan.messages.rules, but I am slightly confused by what to put in. Should it be as below to prevent spam scanning but allow virus scanning:

To: *@domain.com no
From: *@domain.com no
From: *@domain.com virus

Thanks in advance.