Polite behavior for email would be correct grammar and spelling. When emailing a friend it is okay to be casual, but while email a teacher you should introduce yourself, be formal and respectful. Rude behavior for this communication would be using sarcasm, or joking, because the person receiving the email cannot tell you are joking.

Veronica Cargay, Annelise Mahr, Andrew Peters, Kimberly Rosas, Beth Payne