general spam question

can a spambot like rustock infect a computer without an email account setup and still send spam? My ip address has been blocked by spamhaus and I have scanned all of my personal computers with combofix, malwarebytes, superantispyware, avg, vipre, spybot, smitfraudfix, and have looked for it visually thru the registry. I am a tech shop and deal with this stuff on a daily basis and anytime before I hook a customers computer to my network it is scanned with all the aformentioned tools. So unless the bot can send out emails without even having an email client set up, the only thing I can figure is someone is spoofing my hard ip address.

Thanks in advance

 

that's kinda my problem, I rarely use the computer that I have the email on to send email, I usually just use my yahoo account for any correspondence. That's why I was wondering about this. If the spambot could send out email without an account set up, I could get this blacklisted stuff but having an email account only on 1 system and knowing that system is clean.....just blows my mind.