> <em>I understand that a large email blast will generate all kinds of auto-responses, email bounce messages, and other forms of invalid replies, but with some decent filtering and a little work an organization could surely separate the wheat from the chaff. It's the least they could do to in exchange for reading their message.</em>

I don't think the author appreciates how difficult this is. It's just not realistic in all situations, especially situations where the user knowingly signs up to receive an automated message.

I normally use Error-To for do-not-reply, and post a valid reply-to header, but in many scenarios this isn't enough. dpcan's first comment is particularly relevant > "the email address has to resolve back to the sending server properly or the spam filters kill it"