handling spam from gmail.

[Ralph Seichter]

* Marc Roos:

> 3. system recognizes as this email never been seen before
> 4. auto reply with something like (maybe with a wait time of x hours):
>    Your message did not receive the final recipient. You are sending 
>    from a known spam provider

Generating backscatter is definitely not a good move, and it is even
prone to punish yourself. Better to reject the offending message with
a 5xx status code and some explanatory text or the URL.

The various tests required to come to a decision about accepting or
rejecting the message can be executed in a milter. Milter-regex, for
example, is lightweight but still powerful enough to perform tests on
combinations of various headers and the body content. Beyond that, a
custom milter is always an option.

-Ralph