recognizing spam sent by viruses

[Rob McEwen]

Is there some way of knowing for **sure** whether a spam which does NOT actually contain a virus was sent by a virus?   Is there a corpus of such examples anywhere?   Also, do these viruses ever use the SMTP server set up on that computer in Outlook (via Windows registry), or do they always use external third-party smtp servers for sending the spam?   (I’m researching this as a prerequisite to trying some additional anti-spam strategies.)   Thanks,   Rob McEwen