David Doe: Good evening Mr. Smith. I am writing in reference to the job offer that has been posted on XXX. I would like to express interest in the position and ask whether it is still available.
John Smith: Good evening Mr. Jones. I regret to inform you that the position in question has already been filled. However, we thank you for your time and we would like to encourage you to apply in the future.
David Doe: Thank you for your reply. 
David Doe is interested in the job offer posted on XXX but it's not available any more. John Smith encourages David Doe to apply in the future.