OT: Omni Directional hostnames

Sorry for the OT post, but I'm stumped and hope someone here can enlighten me.

When sending to a mimecast users, our mailserver timed out with. Looking at the logs, I see:
Aug 9 07:39:48 smtp postfix/smtp[31712]: 060641011CF: host[] said: 451 Hostname is not authorized - <a href="" title=""></a> [3xVXmRAsN4awNrHIyHCW5Q.us94] (in reply to RCPT TO command)

Looking at the web page referred to in the log entry I find this:
451 Hostname is not authorized Omni Directional hostnames is enabled. Disable Omni Directional hostnames.

I did a web search but can't find any other reference to "Omni Directional hostnames". What are they referring to that they don't like about the sending hostname ( No other domain is rejecting messages based on the hostname and the phrase "Omni Directional hostnames" doesn't seem to be industry standard nomenclature. At least not that I can find in my searches.

I sent a query to <a href="mailto: ... at mimecast dot com"> ... at mimecast dot com</a> which was duly rejected (not awfully surprised):
' ... at mimecast dot com' (<a href="mailto: ... at mimecast dot com"> ... at mimecast dot com</a>)
Your message couldn't be delivered because delivery to this group is restricted to authenticated senders. If the problem continues, please contact your email admin.

Again, sorry for the OT post but if anyone knows what the heck they're talking about I'd appreciate it...



Re: OT: Omni Directional hostnames

By Noel Jones at 08/09/2019 - 13:11

On 8/9/2019 12:15 PM, Kevin Miller wrote:

I'm guessing this is something about FCrDNS for your IP, and/or your
HELO hostname doesn't have an A record matching the IP.

-- Noel Jones