Dear [Recepient first name],
Acknowledgement of Reference: [insert name of applicant]
Thank you for your reference on the above individual. [Name] has now joined [Company] and your appraisal of their performance while employed with your Company was certainly an important factor in our decision.
We will hold your reference confidential and once again, we thank you for your cooperation, and would be pleased to reciprocate the courtesy.
Yours [faithfully | sincerely],
[Sender job title]