Often times when a person finds an email that they just received to be of some value they will want to forward it to their friends.  These friends may also find the email interesting and will forward it to their friends, and so on and so forth.  Most email programs insert the headers including To: and often Cc: by default when you forward a message.  This has the single advantage that everybody knows who already got a particular message.  No need to forward the same mail to the same person twice. 

But including all header information with all other To: and Cc: recipients has overwhelming disadvantages:  

• The message looks horrible, and often the actual content is buried and hard to find between all the email address. 
• You share the email addresses with third parties without the consent of the addresses' owners! I wouldn't want my address given to I don't know who just because somebody forwarded me something that she also happened to forward to 150 other people. 
• Email SPAM!!!  This is one of the ways spammers get your email address. 

The Network Abuse Clearinghouse is intended to help the Internet community to report and control network abuse and abusive users.

Spam-Proofing Your Website - Anyone who operates their own website knows that you need to provide a way for visitors to contact you by email. The big challenge is providing easy email access to your visitors, without letting junk mail (SPAM) flood your email inbox.