Graph API attachment issues

Hi All,

we have an application that is trying to send mails to us with attachments in an image format. However the mails are not being received with attachments in web client or outlook. However only when I forward it as an attachment, I am able to see the image in the attachment.

the issue happens both in OWA and web client. Message header also says the mail has an attachment.

We have checked the application as well, the logs are also confirmed that mails have attachment. 

Any ideas would be appreciated on this ?