Either your computer or another computer that has your e mail address on it, is badly infected with a virus to allow another person to send out thousands of spam e mails a day.
"In 2003, spam investigators saw a radical change in the way spammers sent spam. Rather than searching the global network for exploitable services such as open relays and proxies, spammers began creating "services" of their own. By commissioning computer viruses designed to deploy proxies and other spam-sending tools, spammers could harness hundreds of thousands of end-user computers."
"Most of the major Windows e-mail viruses of 2003, including the Sobig and Mimail virus families, functioned as spammer viruses: viruses designed expressly to make infected computers available as spamming tools"
http://en.wikipedia.org/wiki/spam_%28e-m...
All you can do is be sure that your computer is free of virus, worms and trojans. Here is a good clean-up procedure if your currently are lacking one.
1. Scan for virus and remove (free online scan) with BitDefender
http://www.bitdefender.com/site/home/...
2. Scan for trojans and remove (free online scan) with Ewido
http://www.ewido.net/en/
3. Scan for ad/spyware and remove (free download) with Spybot Search & Destroy
http://www.safer-networking.org/en/spybo...
If your computer is clean, then all you can do is wait until the owner of the infected computer that is sending spam with your address relalizes what is going on and cleans-up his computer.
For further infomation you can Google the word "botnet"
Good luck