Got this message back:
Hi. This is the qmail-send program at yahoo.com.It seems like our relationship is over. And that makes me sad. I think it's the folksiness of "I've given up. Sorry it didn't work out" that adds to the pathos.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
220.127.116.11 does not like recipient.
Remote host said: 551 5.7.1 Recipient Unable to accept message
Giving up on 18.104.22.168.