Chrome: Gmail does an excellent job of blocking spam, but sometimes you want to go the extra mile and prevent some mail from ever reaching your account. BlockSender is a Chrome Extension for Gmail that can trick the sender into thinking your email address is incorrect.
Many spammers won't necessarily recognise the "bounced" email return message, but you do get the satisfaction of doing something to let them know the email isn't welcome. The best case scenario for BlockSender is when an individual is sending you email, and they aren't respecting your request for "do not contact". When they get the bounced message from BlockSender, they will think they have the wrong email address for you. Hopefully after that, they will stop pestering you.
The individual plan only blocks a few emails a month and only on personal Gmail accounts, but is free. The Premium Plan for $US4.99/month for $US29/year has unlimited blocking and works with Google Apps as well personal Gmail accounts. Check out the video above for more.