You can choose Unthreaded and have all of the messages appear in strict chronological order. Choosing Threaded will rethread the posts. You can not send mail to more than 53 accounts at one time. If you have more than 52 students, send out the message to 52 students, and again to the remaining students. Then type your message in the text box.
Several options are available in the Compose Article window.
Clicking this button will send your message. Clicking this button will disable that feature. Forward keeps the message and your comments entirely separate. Replies to the current message, quoting the message in the reply. This option includes the message in the body of the reply, so that reference to the quoted material is easier to see.