Hi Zoho,
You have no PTR record for your secondary mail server.
20 mx2.zoho.com.au 103.91.166.141
ERROR: No reverse DNS (PTR) entries. The problem MX records are:
141.166.91.103.in-addr.arpa -> no reverse (PTR) detected
You should contact your ISP and ask him to add a PTR record for your ips
Please address this problem as soon as your technical team can.
Thanks
Shaun