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).