How do I stop someone else from using my email address fraudulently?

To Yahoo, Recently I sent out 50-60 emails from my address book. I was told by all of the senders that each email also included a message (which I did not write or authorize) that included a link. Many of the links were to pharmaceutical companies advertising...

I cant even do an ebay account because someone used my email address there.

My email address is being used by someone else and they have copied my contacts. How do I stop this

This guy is using my email address and I keep getting these ridiculous emails. It has his name and my email address. What can I do to stop this?

My old address is jchori@sbcglobal.net and is being used by someone who is contacting everyone in my address book. I don't know how to get them to stop.

Canadian Neighbor Pharmacy is sending emails that use my email address as the sender. I looked them up on the internet and found that they have been doing this to other people for a long time. I have changed my password but don't know if this will help...

I keep getting emails from someone with the same email address and they are trying to sell me things.

Several fake emails have been sent to one of my business acquaintances over the past 6 weeks. At first he ignored them, but today he called me to alert me to what was going on. He said that he didn't open them because the introduction/comment looked...