The best response to a job rejection letter is to first read all the contents of that letter. Somewhere down the line, there must have been something that you could have done that could have put you in a better position to get the job you applied for.
If the company has sent you a rejection letter, it might even mean that they could consider you in case of future openings so you should not throw a tantrum about not being deserving and not getting a fair chance.
Sooner or later, you will step into professional life. Be positive that there is something good just around the corner for you and that you will get a good job shortly. So, what you need to do is to write a good response letter to the company that rejected you.
In the response, you should not sound angry or dejected at all. Your words should give the reader the impression that regardless of what happened, the person is willing to know where he went wrong and what he should work on.
If you ask questions and reasons behind your rejection, it will show that you have a strong interest in the job and just because you were rejected initially, does not mean that you won’t try again. This will also make the company wary about your vision and will consider you for future appointments.