Sending IP Adress: 206.123.119.186

Unfortunately it looks like the iprimus may have blocked 206.123.119.186, as I get a 554 status and the connection closes when I try to open up an SMTP session with the provider:

[root@lrwdd2 ~]# telnet mx.syd.iprimus.com.au 25
Trying 203.134.71.81...
Connected to mx.syd.iprimus.com.au.
Escape character is '^]'.
554 mx684.syd.oss-core.net
Connection closed by foreign host.

[root@lrwdd2 ~]# telnet mx.mel.iprimus.com.au 25
Trying 203.134.153.81...
Connected to mx.mel.iprimus.com.au.
Escape character is '^]'.
554 mx684.mel.oss-core.net
Connection closed by foreign host.

Can you try contacting the client via alternate means and ask that she have her provider remove any restrictions against 206.123.119.186 from their end?

I've checked and confirmed the server's IP isn't on any known blacklists and currently has a neutral sender reputation at SenderBase:

This message was created automatically by mail delivery software.

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:

beeches@iprimus.com.au
all hosts for 'iprimus.com.au' have been failing for a long time (and retry time not reached)

---------- Forwarded message ----------
From: Paul Andrews
To: Gaelle Beech
Cc:
Bcc:
Date: Fri, 16 Aug 2019 21:58:54 +0800
Subject: Re: Screenshot 2019-08-16 at 5.50.23 pm