Sometimes, the best response to you can offer to rejection is show that you have some dignity because this shows how professional you are and leaves you open to future opportunities. A response to rejection should always be positive no matter what happens and a response to rejection letter should be written with class as well
Acknowledge that you were in fact rejected for a position or opportunity.
Thank the recipient for taking the time to consider you as an applicant.
Let them know that you would still be interested in future positions or opportunities.
Although I was not selected to start working for your company, I’d like to thank you for taking the time to consider me as a valid applicant to your company and to work for you. I appreciated the talks we had and our time during the interview as I learned a lot about the profession as a whole and I will use your advice to progress myself further in the career. If you have any further feedback so that I may better myself down this career path, please let me know as I’m always looking to improve.