The convention on discussion lists and Usenet newsgroups is that private e-mail should not be publicly posted, but people are occasionally thoughtless or unaware of the convention. And you can wind up defending them to people you never thought the message would reach. Most people learn as small children how to use the telephone and to write letters. Appropriate phone or letter etiquette is second nature to most adults. Most people on your campus, however, have had electronic mail for a much shorter time maybe one to five years.
Many incoming students have their first experience with e-mail during orientation.
Electronic mail is a very new method of communication for most of the people who use it and they're still learning the ropes. As a result, they make mistakes. The list of sins goes on and on. Politely informed of the conventions, most people will be happy to follow them. They just need to know what the conventions are.