You can block an e-mail using spam filters. There are many definitions of spam, but one particularly useful one is the following:

Spam is the electronic version of junk mail, and has been around since the Internet was created. E-mail filters are a way of filtering your e-mail to remove unwanted mail based on a variety of criteria. You can block any sort of e-mail, not just mail of a commercial nature. Blocked mail can be deleted automatically or sent to another e-mail address or script. These filters are quite flexible - some examples are provided after the instruction on how to add a spam filter below. All filters are cumulative.