[PLUG] Postfix: fixing a 'host not found' rejection

[Rich Shepard]

   There is a domain being rejected by postfix because 'host not found.' I
put that domain name in /etc/postfix/rhsbl_sender_exceptions with an 'OK'.
This has resolved the issue for many other domains, but not this one. A
typical log entry is:

Jul  6 04:42:19 salmo postfix/smtpd[20260]: connect from
mail.hornady.com[69.20.192.122]
Jul  6 04:42:21 salmo postfix/smtpd[20260]: NOQUEUE: reject: RCPT from
mail.hornady.com[69.20.192.122]: 450 4.7.1 <barracuda.hornady.com>: Helo
command rejected: Host not found; from=<> to=<rshepard at twodogs.us>
proto=ESMTP helo=<barracuda.hornady.com>
Jul  6 04:42:21 salmo postfix/smtpd[20260]: disconnect from
mail.hornady.com[69.20.192.122]

   Is this a mal-formed message at the sender's end (notice noting in the
from=<> in the 5th line)?

   Please suggest how I can tweak postfix to receive messages from this
domain.

Thanks,

Rich