Attention!

[god_is_disabled]

When someone you know sends you an email, the polite thing to do is to acknowledge it somehow, especially if it contains some substance and/or questions. If they send you a second one after you ignore the first one saying, "what gives?", it is especially polite to respond. If at this point, you still ignore the correspondence, you are not worth a third email, let alone the first.

If you are ignoring the person out of indifference, you are an asshole. If it is on purpose, to see how they will react, you have issues.

That is all.