Your teacher can send it back with a low grade and tell you to do it over. People on the Net may just hit their delete button. The Net is only as friendly and nice as we make it. Don't be annoying. Do not copy the entire response back when you have another question or are sending a thanks.
Many people pay online connect charges and many are paying long distance charges.
Keep your .sig files to 4-5 lines for the same reason. Below is an article from The Network Observer that addresses 'Netiquette from a college professor's point of view. In the Risks Digest 15 .57, Dan Yurman complained about a worrisome new net phenomenon, the practice by college students of using subject matter listservs as sources of first resort for information they should be looking up in their university library. He tells the tale of a college course in which students were directed to do research for term papers on environmental issues using messages posted to Listserv groups. The result was a flood of basic questions being directed to a group of specialists in ecology.