Hi,@Cloud Zubair
Thanks for posting your question in the Microsoft Q&A forum.
The error message you're encountering indicates that the IP address of the server sending the email does not have a PTR record set up or that there is a mismatch between the PTR record and the forward DNS entry. This is important because many email providers, including Gmail, use PTR records to verify the legitimacy of the email server sending the message.
I suggest you contact your DNS provider to add the PRT records.
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.