Inquiry email responses

[imemine]

I sent out inquiry emails to the professors on my list, and I'm beginning to get responses back. My issue though is that I don't know whether it would be more polite to reply back with a brief "thank you" or not waste their time with another email at all. I would assume this depends on whether the professor says they are accepting applications or not? Even still, some of the emails from professors saying they are not accepting apps have been quite nice, and my instinct is to still thank them for their time. 

What are your thoughts?

[PianoPsych]

Well, I struggle with this too. I only replied back to the professors I was most interested in working with.. but I have no idea whether that's the best way to go.

Logically I think it wouldn't matter either way- they probably receive so much email that an extra 'thank you' email from one student is no big deal. Thanking the ones who are nice to you sounds like a great idea ?