Domain names have become very affordable, so many organisations register more than one. As time passes, some of those names may no longer be needed, e.g. because the product or service for which the domain was registered has been discontinued. There are several ways for the registrant to handle such a situation.
Avoid just dropping the domain
The easiest option is to let the registration lapse, allowing anyone to register the domain name as soon as it becomes available. This approach has its drawbacks: the registrant receives no compensation for the value of the domain name, and worse, the name can be used for fraudulent purposes. Holding on to the domain is usually inexpensive and should always be considered.
Redirection to a current website
If you decide to keep the domain name, one thing you can do is redirect it, such as to the main website of your organisation. Using a permanent redirection (HTTP status code 301) tends to do the most good in terms of search engine traffic. You are essentially transferring web visibility from one domain name to another. If possible, redirect your most popular and important web addresses (URIs) to specific pages on the new site. In any case, ensure that all other requests are served by returning e.g. the front page instead of a ‘not found’ message. If you use the Apache web server, the mod_rewrite module can be very useful in this respect. You can keep your domain name redirected for as long as you want, but you probably should redirect for at least a few months so that your frequent visitors will be able to notice that the domain is going away.
Parking or selling a domain name
In some cases, you may want to disconnect a domain name from your web presence while still keeping the name under your control. You can simply remove the name server records for the domain, but this course of action does not enable you to generate income from the domain name. A better solution may be to park the domain. This means that you point the domain name to a provider that serves a page containing dynamically generated links and a search box. Visitors arriving at that page will be able to continue their search and you will be paid per click. Finally, you may choose to sell the domain name.