Write a letter acknowledging receipt of application.

Dear sir,

This is to inform you that we appreciate your interest in being employed by our firm. However, it is with regret that we inform you that the available position(s) has been filled, and we cannot give your application further consideration at the present time.
We would like to assure you that your application will be kept on file for future reference and we will consider your case in case of a vacancy.

Thanking you


Yours truly,