An autoresponder is an automatic or software-mailing program.
Why would you want that?
Because whoever you are, you don't have enough time, and an autoresponder will maximise your time potential.

Go to sleep and have a software servant take care of business. Once configured, it will store, send and reply.

That's just great, but is that it? No.

Depending on the price and particular program, autoresponders will vary with respect to function, usability, and features. Free autoresponders are commonly available but can run in advertisements, as well as the information that you wish to send. That is not a completely repulsive concept, given the price, and as good a way to experiment with an autoresponder, as any.

Anyone wishing to access specific information can mail to a specific autoresponder address, but the primary difference is that an autoresponder is not a person, but a delivery mechanism for a person, with no regard for the location, state of awareness, or other demeanour of such a person.

That email that you can get with