[a3_nm]

Pretending to accept an email and then dropping just seems wrong. Is this something that reputable email providers do?

(From my experience, I have never witnessed a situation where an email I had sent to someone had silently been ignored.)

[jimktrains2]

Yes, it is a practice that big players do.

http://serverfault.com/questions/364132/postfix-says-mail-se...

[a3_nm]

My understanding of this answer is that the SMTP said it had accepted it, but the sender would have been notified afterwards that the message had not been delivered, had the return addresses correctly been set up. This seems OK to me; I would have received the bounce.

(Also, the mail was sent from www-data, which I think was an acceptable clue to classify the message as spam no matter from which server it came from.)

[jimktrains2]

It doesn't always need to send a bounce if it doesn't want to.