I get asked by clients what the best way to send post-interview thank you notes is - email or snail mail. I strongly advise sending your thank you note by good old USPS. The reasons are:
1) Email may be viewed as lazy. Hand-written notes demonstrate you've put some time into being appreciative.
2) Email can be deleted without much thought. Emotionally, it's harder to throw someone's hand written note in the trash.
Get your handwritten thank you notes in quickly. The night after you've completed your interview or the next day is a good time to write and send.
