One trick for dealing with unwanted email messages is to bounce them. This acts like stamping a "Return to Sender, Addressee Unknown" notice on the front of your received message. When you bounce an email message, the sender receives the bounced message, which makes your email address appear invalid.
Bouncing a message back to the sender works only if the sender's return email address is correct. Since many people and companies send junk email (known as spam) using fake email addresses, bouncing a message back to a fake email address will just return the bounced message back to you again.
Because of this, you should bounce a message only when you know the sender's email address is valid. For example, you can bounce a message sent by someone you don't like anymore (such as an ex-boyfriend or girlfriend).
Here's how to bounce a message:
Start Mail. (Click the Mail icon on the Dock, or double-click the Mail icon in the Applications folder.)
Click the message you want to bounce.
Select Message ▸ Bounce. A dialog appears, asking if you want to bounce the message.
Click Bounce. Mail moves the message into your Trash folder and sends a bounce message back to the sender.