When I receive an e-mail from an automated virus-scan telling me I sent an infected e-mail, I investigate.
First, I read the notice. If it identifies the virus, I look it up. I make note if it spoofs addresses. If a copy of the e-mail is included, I examine the headers to see for myself if the address is spoofed. I then update virus signatures and perform a scan. My computers have yet to be infected, but I double-check.
Once I determine the address has been spoofed, I send an e-mail to the site that notified me. I ask them to please reconfigure their auto-notify to not send messeges to spoofed addresses.