This is an automatically generated Delivery Status Notification
Delivery to the following recipient failed permanently:
Technical details of failure:
PERM_FAILURE: SMTP Error (state 10): 554 The IP Address of the sender (18.104.22.168) was found in a DNS blacklist database and was therefore refused.
[Brian S. - I was trying to mail you, nothing important]
Coincidentally yesterday I realised I hadn't heard back from someone I'd mailed a week ago, the original mail having been bounced a bit first through one of his colleagues. I went back to check and found it had gone out with the subject line "Delivery Status Notification (Failure)".