SES service not able to deliver mails from my stenum-asia.org mail id

I have activated the SES service for my lightsail instance and for some reason whenever the email transmission is happening, the Mail is not getting delilverd , but instead it is going into the spam folder of the sender's email account.

Delivery Status Notification (Failure) External Spam MAILER-DAEMON@ap-south-1.amazonses.com

The above is the info I receive from the spam mail.

But when i changed the sender's mail id to my gmail account , the mail was delivered without any problem. Can someone please let me know what might be the issue with our account or with our email domain address..