With a simple filter, Gmail can send all incoming mail from your favorite forwarders to theTrash folder as it arrives. As an alternative, you can archive these messages and equip the with a label for later review.
Block a Sender in Gmail
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 firstname.lastname@example.org and email@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 firstname.lastname@example.org and email@example.com by typing "firstname.lastname@example.orgemail@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) andApply the label: under Choose action when setting up the filter.
Add a New Address to Your Gmail Block List
To add new senders to your block list, add them to an existing deletion filter using "|" (as above), or create a new filter if the From: field has grown big and unwieldy.
source : http://email.about.com/