SMTP Transmission Failure

Delivery Failures for mail I did not send - Spoofing or Trojan

I'm getting delivery failures for email I didn't send. It's probabaly someone spoofing my account, but could it be a trojan sending emails directly via SMTP? How can I tell? Is there a way to query the SMTP service for a list of sent emails?

SMTP transmission failure has occurred

the following massage i am receiving from long time this is come mostly when i send to yahoo mail server please tell what reasons????????? Your message cannot be delivered to the following recipients: Recipient address: amit_filex@yahoo.com Original address: filex@vsnl.com Reason: SMTP...