Final answer:
An open e-mail relay is bad because it allows anyone to send spam through the server.
Step-by-step explanation:
An open e-mail relay is bad because it allows anyone to send spam through the server. When a server is an open relay, it means that it does not check the origin of the e-mail and anyone can use it to send messages. This can lead to a flood of unwanted and potentially harmful spam emails. Open e-mail relays are commonly used by spammers to hide their identity and distribute spam.