There is no standard for this. Beyond that, why would you want to be standard - the point of an interview is to come across as exception. Figure out each indivi

There is no standard for this. Beyond that, why would you want to be standard - the point of an interview is to come across as exception. Figure out each individual person, and send as many as you can remember/find/track a hand-written, mailed thank you letter. The whole point of the post-interview thank you is to be remembered, so if your tactic isn't memorable it isn't worth doing.