> E-mail is actually a good example of why you shouldn't open up communications systems too much. Because they're more or less free to send, people who want to

> E-mail is actually a good example of why you shouldn't open up communications systems too much. Because they're more or less free to send, people who want to send advertisements send loads of them. This makes e-mail entirely unusable unless you are very proactive in restricting who can send mail to you. Technical limitations like SPF, DKIM, and so on only prevent the worst abuses. What does really work has been IP blacklisting and reputation systems that more or less make rolling your e-mail very difficult. Unfortunately the real problem with email is liability. There's no way for me to force liability of a received email onto the sender. I can't tell Gmail to block all non-US email. I can't even tell Gmail to block all mail from specific IP blocks or domains. If malicious email originates from the US then there's some very strict laws around malicious use of computers... A phone call though? The liability is in the caller or, at least, the service provider.