Not long ago, if an employer wanted to have a prospective employee interview for a job, he would have his secretary call the person in question and set up an interview date. In today’s modern age, not all interview invitations are made with a simple phone call. Employers are more likely to send their prospective employees an invitation through email or through the postal service. However you receive your interview invitation, a timely response is necessary.
Respond to the RSVP invitation for an interview using the same medium that your prospective employer used, unless it specifies otherwise. For example, if you receive an invitation via email, respond with an email. If you receive an invitation via postal mail but are requested to call to confirm, only a phone call would suffice.
Note the "RSVP by date" on the invitation. While the company could have given you several days to RSVP for the job interview, the sooner you respond the better. Leaving the response to the last minute makes you look like a procrastinator.
Address your RSVP to the person who signed your invitation. Getting the name wrong looks very bad.
Keep the response short. Thank him for the invitation, and agree to meet at the designated interview time. The response email or letter should be signed "Sincerely," then your first and last names.
If you cannot make the interview time, need to reschedule or do not wish to apply for the job, still respond to the invitation. Thank the sender for the consideration, declining politely. This way, you look professional and won't have burned any bridges.
When responding via email, look for an alternative email address within the invitation. Clicking on reply might not get your email to the proper location.