E-mail blacklists guarantee that the user will not receive e-mail from a certain party who is or is suspected to be a spammer. Blacklists work with various kinds of spam guards, and some block more throughly than others. The user decides who to blacklist, and unless the user is blacklisted, the software can never ban a message entirely, but send the doubtful message to a bulk folder.

However, a whitelist can refuse to allow someone entry if he or she does not enter the code correctly. Nevertheless, most are allowed another attempt and are not blacklisted unless the user initiates the action. The exception to this rule is when known spammers are barred from using internet and e-mail service from the provider. This is used as a protection for all e-mail users.

In spam filters, black lists work by allowing the user to block certain e-mail addresses or keywords in e-mails. Most e-mails that spam filters suspect as spam because they contain keywords common to spam e-mails, are filed in the bulk folder for the user to review.

Periodically, this bulk folder is automatically emptied unless the user want to keep the message. Whether the spam appears in the bulk folder or somehow makes it past the filter into the inbox, the user can mark the suspected e-mail as spam, and blacklist that sender.

Spam blockers offer a higher degree of protection, and like spam filters, place all suspected spam in a quarantine folder. With spam blockers, almost all e-mails are presumed to be potential spam until the user approves certain e-mails. Like spam filters, once an address is blacklisted, the e-mails no longer appear even in the bulk folder, but the messages are bounce back to the sender.

Whitelists require all potential senders to register first by typing in a partially obscured code that cannot be detected by spam software. If someone fails to gain entry, they cannot send their e-mail, but they are not blacklisted unless the user specifies that this address should be blacklisted.

While blacklists are necessary for spam protection, there can be serious problems that result form blacklisting in cases where one's computer is being used as a spam zombie. Spammers want to escape recognition, and many have the technical knowhow to use spyware to obtain private information about a client and data bout his or her PC.

If your PC is unprotected, you are making yourself vulnerable to spyware, which can allow hackers to infect your computer with a virus or to obtain your information to use your computer as a spam zombie, forcing your PC to send out unsolicited spam to hundreds or thousands of people.

Many innocent people have been barred from e-mail providers, lost their internet connections, have been blacklisted by countless people and have faced fines or even jail time. Once a person has been blacklisted, it is difficult to regain one's former status, and this happens often to people who are victims of spammers and whose PCs become spam zombies.

However, since this problem is becoming more widespread, there are possibilities for mending one's status after having been blacklisted as the result of becoming a spam zombie. The process takes time, but sometimes the blacklist status is reversible.