What is an open mail relay and why is it a problem?
An open mail relay is an email sending server program that is configured in such a way that it will allow people off-campus to send mail through it to other people who are also off-campus. In general, mail sending servers should only accept email destined to or received from their local machines. Sendmail is the most popular UNIX mail transport agent. It’s not the program you use to read your mail, but rather the program that ultimately sends and receives the mail. In fact, sendmail is two programs. As a server daemon, it receives mail (and can also resend the mail it receives); but invoked as a normal program, it just sends mail that you composed. Its usage as a daemon is problematic if not configured properly, but just using it to send mail from pine or elm or mail is OK.
