A thank-you email is purely for my ego ... If it's not online or you don't have someone's business card, email the person at the company who set up the interview and ask for the address.

Sending a thank-you email within 24 hours of an interview shows professionalism and reiterates your interest in the position. Customize your thank-you interview emails based on the person's title ...

See, throughout his tenure at the company, Conant sent more than 30,000 handwritten thank-you notes to staffers and clients. (In a 2011 Harvard Business Review article, Conant explained that he ...