Graph Mail api - data-attributes are deleted when working with drafts

Question

I'm working with Graph api to create and manage draft messages on outlook.
I'm generating an HTML body and trying to add data-attributes on an element in the body.
But when I create/update the draft, my attribute is being deleted and the draft message is saved without it.

For example, if I use:
POST https://graph.microsoft.com/v1.0/me/messages (using create message api - https://learn.microsoft.com/en-us/graph/api/user-post-messages?view=graph-rest-1.0&tabs=http)
with this body:
"body":{
"contentType":"HTML",
"content":"<div data-my-var="value"> This element has a data attribute </div>"
}
My data-my-var attribute is being deleted and the body I get in the response doesn't have it

I'm building my own email editor which is integrated with office and I don't want to lose my special attributes after creating/updating the draft on the mail provider.

Is there any way to make this work or any alternative approach?