I asked a question at Ask Ubuntu. A user posted an answer and comment. But I did not receive any email notification of the response.
In preferences, I have email id set, Inbox emails and Other emails checked.
Emails are not sent as soon as someone posts an answer or comments.
Emails in Stack Exchange websites are more like digests.
The way they work is, if you don't check your notification messages (The ones in the top left, where it says `StackExchange) for a certain amount of time (depending on your preferences), you get an email saying:
1 new item in your Stack Exchange inbox
Of course it's not always 1, it's just as many items as there are in your inbox.