On blocking Internet mail from dynamic addresses

Some mail servers on the Internet are configured in way that makes them treat all traffic that comes from a dynamic, or private, addresses as spam. They reject the transaction with a status code and close the connection.

This is not a solution to the problem of spam. Locking yourself down by building walls is not a solution. It is actually admitting defeat that you cannot solve it, giving up on looking for an answer to the problem at hand. It is showing your back on the problem and behaving like it does not exist.

It is simply patethic.