In computing, a blacklist or block list is a basic access control mechanism that allows through all elements (email addresses, users, URLs, etc.), except those explicitly mentioned. Those items on the list are denied access. The opposite is a whitelist, which means only items on the list are let through whatever gate is being used. A greylist contains items that are temporarily blocked (or temporarily allowed) until an additional step is performed.
For example, a company might prevent a list of software from running on its network or a school might prevent a list of web sites from being accesses on its computers.
Information systems
The opposite of whitelisting, blacklisting allows everything to run unless it is on a predetermined "blacklist". A blacklist includes certain types of software that are not allowed to run in the company environment. For example, a company might blacklist peer to peer file sharing on its systems. In addition to software, people, devices and Web sites can also be blacklisted.
Most email providers have an anti-spam feature that essentially blacklist certain email addresses if they are deemed unwanted. How this happens is when a successful phishing attack (from an address that is forged from reliable accounts to try to recover personal information) is executed, then the email device deems the address to be spam, and proceeds to blacklist the address.
To see if your domain is blacklisted, click HERE.
