Below is what the client sends me.

-----Original Message-----
From: Mail Delivery System <Mailer-Daemon@you.yougodesigns.com.au>
Sent: Monday, 17 June 2019 4:47 PM
To: ericc@themoneypeople.com.au
Subject: Mail delivery failed: returning message to sender

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:

  david@capitol.com.au
    host capitol-com-au.mail.protection.outlook.com [104.47.116.36]
    SMTP error from remote mail server after RCPT TO:<david@capitol.com.au>:
    550 5.7.1 Service unavailable, Client host [202.131.88.1] blocked using Spamhaus. To request removal from this list see https://www.spamhaus.org/query/ip/[202.131.88.1] (AS16012611)

It seems to be blocked by ] blocked using Spamhaus

If I do a blacklist check on our servers ip address  202.131.88.1 it appears on a few blacklists.

https://mxtoolbox.com/SuperTool.aspx?action=blacklist%3a202.131.88.1&run=toolpage

Can you please help.