Check and see if your ISP has changed the rules about how to send email from your computer
Check and see if some how the send login information got messed up.
2) Someone is faking that the emails are coming from you. Spammers do that. They have probably got your email id from someone else’s infected machine or off the net if you posted it there.]]>
Some blogging software does that to try and avoid spam being posted to their blog/website.
The other thing that could have happened is that you typed your email address incorrectly and in the background programming it checked that it was a valid email address before processing the form.]]>