Gmail doesn't provide any real blacklist function, but instead provide several filters to block unwanted emails. Indeed emails from unwanted senders are redirected to the trash.
The procedure is as follows:
Sign-in to your Gmail account.
Click on the small arrow button located to the right side of the search bar.
In the From field enter undesired e-mail address. You can also block entire domains (@domainname).
Click on Create filter with this search.
In the new window that opens up, select the "Delete" action.
Click on Create Filter.
As from now, emails sent from the define address will be automatically deleted.