I forgot to add:
Sending an email thank you is just fine and is an acceptable replacement to sending a hand written thank you note via regular snail mail. The email does not have to be very long. Just a couple of sentences is sufficient. Something like this is probably ok:
"Dear ____,
Thank you so much for speaking with me earlier today/yesterday about my application to _NameofCollege. It was a pleasure meeting you. I am very excited about the opportunity to ___ (say something about your major, areas of interest, or anything you want to say about College X) at College X. Thanks again for your time.
Sincerely,
First Name, Last Name
email address
phone #"