It's important to send a thank you letter after a job interview. If at all possible, send your thank you note within 24 hours of interviewing. If time is of the essence, send your thank you letter via email.
It's important to say thank you after a second interview, as well as after the first, so, don't forget those letters either.
When you have a group interview, thank all the people that you met with. If you're not sure who everyone is, check with the person who scheduled the interview.
Thank You Letters