To have Gmail send messages from a specific sender to the Trash automatically:
1. Click the Show search options triangle in the Gmail search field.
2. Type the desired email address under From:.
(a) You can block an entire domain by entering just that. To block all mail from both email@example.com and firstname.lastname@example.org, type "@example.com".
(b) 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 email@example.com and firstname.lastname@example.org by typing "email@example.comfirstname.lastname@example.org", for example.
3. Click Create filter with this search ».
4. Make sure Delete it is checked under When a message arrives that matches this search:
5. Click Create filter.
(a) Check Also apply filter to __ matching conversations to delete previously received messages.