Hello Vignesh S,
Thanks for reaching out. To assist you better please provide the Graph API you are using to reply to emails. For your reference the article https://learn.microsoft.com/en-us/graph/api/message-reply?view=graph-rest-1.0&tabs=http provides details on replying to a message using Graph API.
If the reply is helpful, please click Accept Answer and kindly upvote it. If you have additional questions about this answer, please click Comment.
Thanks.