Whitelist is a term used to describe a list or register of entities that, for one reason or another, are being provided a particular privilege, service, mobility, access or recognition. As a verb, to whitelist can mean to authorize access or grant membership. Conversely, blacklist is a term used to describe a list or compilation that identifies entities that are denied, unrecognised, or ostracised.
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An e-mail whitelist is a list of contacts that the user deems are acceptable to receive email from and should not be sent to the trash folder.
Spam filters that come with e-mail clients have both whitelists and blacklists of senders and keywords to look for in e-mails. If a spam filter keeps a whitelist, mail from the listed e-mail addresses, domains, and/or IP address will always be allowed.
Some internet service providers have whitelists that they use to filter e-mail to be delivered to their customers. ISPs receive requests from legitimate companies to add them to the ISP whitelist of companies. Companies either pay for a time period to be allowed to e-mail their customers or the companies pay per complaint received by the ISP from their customers. These payments per complaint increase incrementally; i.e., the first 10 complaints are $10 each, then the next 10 are $20 each. These funds are then used by the ISPs to fund anti-spam programs to prevent unwanted e-mail.
If a whitelist is exclusive, only e-mail from those on the whitelist will get through. If it is not exclusive, it prevents e-mail from being deleted or sent to the junk mail folder by the spam filter. Usually, only end-users would set a spam filter to delete all e-mails from sources not on the whitelist, not internet service providers or e-mail services.
Using whitelists and blacklists can assist in blocking unwanted messages and allowing wanted messages to get through, but they are not perfect. E-mail whitelists are used to reduce the incidence of false positives, often based on the assumption that most legitimate mail will be from a relatively small and fixed set of senders. To block a high percentage of spam, e-mail filters have to be continuously updated as e-mail spam senders create new email addresses to e-mail from or new keywords to use in their e-mail which allows the e-mail to slip through.
Non-commercial whitelists are operated by various non-profit organisations, ISPs and other entities interested in blocking spam. Rather than paying fees the sender must pass a series of tests; for example, his email server must not be an open relay and have a Static IP address. The operator of the whitelist may remove a server from the list if complaints are received.
Commercial whitelists are a system by which an internet service provider allows someone to bypass spam filters when sending e-mail messages to its subscribers, in return for a pre-paid fee, either an annual fee or a per-message fee. A sender can then be more confident that his messages have reached their recipients without being blocked, or having links or images stripped out of them, by spam filters. The purpose of commercial whitelists is to allow companies to reliably reach their customers by e-mail.
Commercial providers include GoodMailSystems's Certified Email, Return Path Certification,[1] eco's Certified Senders Alliance, and the Spamhaus Whitelist.[2]
Another use for whitelists is local area network (LAN) security. Many network admins setup MAC address whitelists or a MAC address filter to control who is on their networks. This is used when encryption is not a practical solution or in tandem with encryption. However, it's sometimes ineffective because a MAC address can be faked.
Some firewalls can be configured to only allow data-traffic from/ to certain (ranges of) IP-addresses.
If an organization keeps a whitelist of software, only titles on the list will be accepted for use. The benefits of whitelisting in this instance are that the school administration can ensure itself that students will not be able to download and/or use programs that have not been deemed appropriate for use.
An emerging approach in combating viruses and malware is to whitelist software which is considered safe to run, blocking all others.[3] Some deem this as superior to the standard signature-based, anti-virus approach of blocking/removing known harmful software (essentially blacklisting), as the standard approach generally means that exploits are already in the wild.[4][5]
These products may provide administrative control over program whitelists in addition to preventing introduction of new malware,[6] but they cannot stop exploitation of existing processes in order to gain root (and therefore bypass/disable the whitelisting application.[7]
Among Unix Operating system variants, HP-UX has introduced a feature called "HP-UX Whitelisting" on 11iv3 version. HP-UX Whitelisting (WLI) offers file and system resource protection based on RSA encryption technology. WLI is complementary to the traditional UNIX discretionary access controls (DAC) based on user, group, and file permissions. The more granular DAC access control list (ACL) permissions available on VxFS and HFS file systems are likewise not affected.