Bounce message received:
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:Malformed SMTP reply from mail.server.com [192168.1.1]
in response to initial connection:
rblsmtpd: 192.168.6.62 pid 14483: 451 Sender has sent to LashBack
Unsubscribe Probe accounts:
retry timeout exceeded
Looking further into this it appears that the sending IP address was listed in a RBL black list. The RBL server being queried was: ubl.unsubscore.com
This in turn (www.unsubscore.com) took me to: http://www.lashback.com/support/UnsubscribeBlacklistSupport.aspx
Most RBL systems return a useful message with a URL, but, not lashback.