Verified answer

If you are using Yahoo Classic:

Go to "Options" (It is above your E-mail) >Click on "Mail Options">Click on "Blocked Addresses". Enter the address you want to block>Click on “Add Block”>Click on “Save”

http://help.yahoo.com/l/us/yahoo/mail/classic/abus...

If you are using New Yahoo Mail

Go to "Options" >Click on "Mail Options">Click on "Spam". Enter the address you want to block>Click on “Add ”>Click on “Save Changes”

http://help.yahoo.com/l/us/yahoo/mail/yahoomail/co...

Click on options, then go down to block addresses.

definite you may provide up them from sending you those nasty emails . you may record them to yahoo and also you'll mark any messeges from them and performance it despatched to ur bulk messeges and dumped without searching at it .