It's P3Scan that replaces the original e-mail with the text to say it was a virus. I'm assuming you mean is that it currently can't do that. It probably could, if someone wanted to resurrect the code and enhance it, as development ceased some time ago.
That's how I did it in NS6, but switched to P3Scan in NS7 so I didn't have to create a user for every e-mail account I wanted to retrieve from.
How is anti-virus handled in this scenario.
Clients are Thunderbird and Outlook, and as it's P3Scan it has to be POP3.
Not really an option. Also see above as to why I switched to P3Scan.
I realised after @filippo_carletti's comment, that the Junk folder I was used to seeing was when using the POP3 connector which means there are "real" mailboxes on the NS server and so the mail can be moved to a Junk folder. P3Scan is effectively a pass-through.
Except I am NOT seeing ANY mail with that prefix.