Here is an example of a letter sent via email to accept and confirm a job interview.
Letter Accepting Interview Invitation
Subject Line of Email Message: Interview Confirmation - Sara Potts
Dear Mr. Gunn,
Thank you very much for the invitation to interview for the Account Analyst postion. I appreciate the opportunity and I look forward to meeting with Edie Wilson on June 30th at 9 AM in your Quincy office.
If I can provide you with any further information prior to the interview please let me know.