Here’s an email I received:
I apologize for this automatic reply to your email.
To control spam, I now allow incoming messages only from senders I have approved beforehand.
If you would like to be added to my list of approved senders, please fill out the short request form (see link below). Once I approve you, I will receive your original message in my inbox. You do not need to resend your message. I apologize for this one-time inconvenience.
Click the link below to fill out the request:
Someone sent spam to this person, forging my email address as the sender. This person never saw the spam — they dumped it on me. So not only do I have to deal with my own spam, I have to deal with theirs too! Challenge-response spam filtering is a selfish approach to fighting spam.
I filed a complaint with their ISP.