You've probably seen email capture forms similar to that shown in the graphic here to the right at least a million times.
When someone enters their name and email address, it triggers an autoresponder.
The autoresponder automatically responds (ergo, the name ‘autoresponder') by sending a preprogrammed / prewritten message to the email address entered in the form.
Autoresponders are sometimes used by individuals to notify those who send them emails that they are away on vacation, i.e. an ‘out of office‘ reply is sent.
Autoresponder services are more commonly used by online businesses to build client mailing lists and to provide their web site visitors with followup and new information about their products and services.
Autoresponder service features most often include the ability to preprogram an unlimited number of prewritten followup responses that are sent at predetermined intervals. For example, the first message is sent immediately after a person subscribers, the second message is sent 2 days later and message number 3 is sent three days after the second message… and so on and so forth. This is known as an ‘autoresponder series'.
Autoresponder service clients may also send out broadcast messages to their subscribers on an ad-hoc basis.
In recent years, autoresponder services have added a feed to email feature that allows webmasters to send published posts from their blogs (and other feeds) to their mailing list subscribers.
Although there are many autoresponder services available, I personally recommend Aweber – a service that I've been using without complaint since starting my online business in 1998. Aweber is without a doubt, the world's leading autoresponder service in terms of features and customer service.