As a teacher, can I set up Email accts for my students so they can ONLY email to students within the class?

Well, it depends.





What you can do is set up a club or group like at www.meetup.org





Then your students are given IDs and made members of the group. They can participate in message threads that everyone in the group can read and can send each other private messages that no one else can read. No one who isn't a member of the group can even see who is in there let alone what's going on.





You can set up email accounts but filter out all messages from all sources except a "white list" of other students. But that's not foolproof and your kids will learn how to defeat it.





If the computers are in school and not in the student's homes, you can set up an intranet environment which doesn't even interact with the internet so no outside stuff can get in.





But, if the computers are in the homes, there is little you can do to make sure the kids are not exposed to strangers. The kids will find a way if they want to. And they will want to.