In contemporary western culture is an email an acceptable format for a "thank you" note?

Yes, in contemporary western culture, and email is acceptable. The majority of people who even both to send thanks use email. But, do you really want to settle for acceptable, when you could do better?

I've interviewed a lot of candidates over the years, and I've received a lot of thank you notes. The ones that really stand out were hand-written on note paper, and it was clear that the writer had put some real thought into them. Often they thanked me, but they also emphasized details that had come up during the interview which they wanted to expand on. The best candidates sent an email immediately with quick thanks, then also followed up with a longer, paper thank you note.

Send emails if you want to meet minimum acceptability standards. Do better if you want to stand out from the crowd.

In contemporary western culture is an email an acceptable format for a "thank you" note?

Yes, in contemporary western culture, an email is acceptable. The majority of people who even bother to send thanks at all use email. But, do you really want to settle for acceptable, when you could do better?

I've interviewed a lot of candidates over the years, and I've received a lot of thank you notes. The ones that really stand out were hand-written on note paper, and it was clear that the writer had put some real thought into them. Often they thanked me, but they also emphasized details that had come up during the interview which they wanted to expand on. The best candidates sent an email immediately with quick thanks, then also followed up with a longer, paper thank you note.

Send emails if you want to meet minimum acceptability standards. Do better if you want to stand out from the crowd.