To have Gmail send messages from a specific sender to the Trash automatically:
Follow the Create a filter link (at the top of any Gmail mailbox, near the search buttons).
Type the desired email address under From:.
You can block an entire domain by entering just that. To block all mail from both natsuko@example.com and pjotr@example.com, type "@example.com".
To block more than one address, separate them with "|" (the vertical bar; typically above the backslash on the keyboard; not including the quotation marks). You can block both natsuko@example.com and pjotr@example.com by typing "natsuko@example.com|pjotr@example.com", for example.
Click Next Step ».
Make sure Delete it is checked under Choose action.
Click Create Filter.
Check Also apply filter to __ conversations below to delete previously received messages.
To archive and label instead of delete messages, choose Skip the Inbox (Archive it) and Apply the label: under Choose action when setting up the filter.