Why email from my whitelisted sender has been blocked?
Network Box systems which handle emails, are usually configured to scan for:
These scans are treated as separate, and are therefore separately configurable.
Just because a sender is whitelisted (either globally or personally) it does not automatically follow that emails from them will not be scanned for "malware," or "company policy violations." There is no reason a virus should be let through, just because the sender was whitelisted for Spam.
In the same way, "company policy violations" are not allowed, just because a sender is on a Spam whitelist. Take for example, "active code," included inside an email. If this were allowed just because the sender was whitelisted for Spam, the receiver would be put at risk, because there is always a chance that the "active code" is a threat.
It is entirely possible for Network Box to enable, or disable, any of these three types of scan. But it is very important to realize that disabling either the malware scanning, or the company policy scanning, will increase the risk of the recipient of an email becoming compromised.