Should I send a thank you note via snail mail after a first interview?

Thank you emails are appropriate/sufficient these days, at least in my experience. So much of the hiring process is online that I think sending letters via postal mail will only confuse matters. (What if your note gets lost and they only receive it after you have another interview, or don't see it at all, or something? Sort of related anecdata: one time I snail-mailed an application and someone replied they were interested in hiring me 5 months later, long after my ability to take the job had passed.)

Thank you emails are totally appropriate

I was up for a job I really wanted a few months ago. I sent a snail mail note, and it was returned to me because the mail for the company went to a PO Box, and not the physical address where I went to interview. I regret not using email.

Just the thank you email. I used to be very much "still snail mail!" but really, things move too fast these days for that. The whole point of the thank you note originally was to show that (a) you're grateful and (b) you're prompt. The email thank you note still doe that - the snail mail one leave them wondering about the "prompt" part for days longer than you really want.

I guess this is an American thing, as I've never heard of a "thank you" note being sent after any kind of interview ever.

You don't say what type of business you interviewed at. If this was a tech company, a snail mail letter would be seen as fairly odd.

Just write a handwritten note and mail it or better yet drop it off at the front desk. It's not overkill it's thoughtful. I send an email of course. One time I came back for the secind interview that I already had set up to see the thank yiu card I sent on display behind my interviewers desk. Because of all the commenters before me, physical mail is treasured. So my note was treated as a special kind of statement.

Next time just bring the thank you card and fill it out and drop it off before you leave.

I agree with yoink.