Spam is unsolicited e-mail. There are numerous techniques that can help reduce the amount of spam a person gets, though it can be very difficult to stop spam altogether. In most cases, using a variety of techniques together will have the best results. These can include using multiple e-mail accounts, avoiding publishing e-mail addresses online, and using commercial tools.
One method to stop spam is to limit the availability of your e-mail address online. This is because spammers can set their machines to scan websites to hunt for e-mail addresses. If you do need to publish your e-mail address, it may be safer to write it in a format that can be understood by humans but not detected as an e-mail address by machines. One example of this is "nospam AT wisegeek DOT com," which a human can translate into the standard e-mail address format.
It is best to avoid replying directly to spam messages. This is because many spammers simply send messages to every possible combination of letters and numbers that make up an e-mail address. Replying lets the spammer know your address is genuine and you check your inbox. This makes your e-mail address much more valuable and may increase the chances of them selling your address on to other spammers.
Many e-mail providers offer tools designed to stop spam. Look for a provider that has a simple one-click button that lets you report a message as spam. Usually this will mean that future messages to you from that address, or sometimes similar addresses as well, will be filtered out so that you do not receive them. In some cases, if several people report messages from the same address, the e-mail provider may block all messages from that address from reaching any of its customers.
Some techniques do not stop spam, but rather limit its effects. This includes the practice of setting up a second e-mail account, usually a web-based e-mail service, to be used solely for registering for websites. Doing this means that any resulting spam does not go to your main account. If you use this technique, it is best to forward any legitimate e-mails, such as ones confirming your registration or log-in details, to your main e-mail address. This will make it easier to locate and retrieve the details later on, rather than having to wade through the spam on the second address.
There are some commercial services that aim to stop spam. These work online and will effectively intercept your incoming messages and filter out anything that appears to be spam before passing the other messages on. It is arguable whether these offer any more protection than that offered by the best e-mail providers as part of their service. Some of these commercial services work by replying to the sender asking him to confirm the message is genuine and to type in a code shown in an image, which blocks a computer from automatically replying. While this technique will stop spam, it will irritate many legitimate senders and won't be of use for automated messages that are not spam, such as e-mail newsletters to which you subscribe.