Block a Particular Sender's Messages
Set up a rule to deal with them so you never see them.
For regular mail messages, go to Tools -> Rules / Mail tab. Click New and enter the following:
IF From Contains (click Add Criterion in order to enter more)
THEN Move message (to) Deleted Items (remove any unwanted additional criteria and click Enabled).
For newsgroup messages, go to Tools -> Rules / News tab. Click New and enter the following:
IF From Contains (click Add Criterion in order to enter more)
THEN Do not show article (remove any unwanted additional criteria and click Enabled).