On the other hand, simply providing this service enables anyone, malicious or not, to determine if a given mail server is vulnerable. Publishing a "shame list" doesn't reveal any new information, but may result in improvements to the vulnerable servers as a result.
I agree, it's also not that great to have a list of "Insecure web servers" [0], there should be a "don't show checked site in public results" checkbox like on ssllabs.com's certificate tests.