While there's nothing that prevents people from sending a spammy message, we did recently start to collect responses from people that mark a message as "not interested". In your case that would be: "This position does not appeal to my interests at all". We use this feedback as a quality indicator, and will take action if we see that an employer is abusing the service, up to and including refunding and canceling their subscription (although that would be a final measure, we'd much rather have them see the light and start sending well targeted and interesting messages). Over time we'll work to fine tune this quality feed back mechanism.
Also, forwarding a spammy message to firstname.lastname@example.org is a good way to get us to look at it.
W/r/t the message you received, we'll look into this employer to see how their messages have been received. Thanks for pointing it out!