Hi @-- --
This problem occurs due to the lack of corresponding parameters when sending the request, if you want to use the graph client to send an email, you can send it according to the code below.
await graphClient.Users[SenderUserEmail].SendMail.PostAsync(requestBody);
Here you need to add the argument from the SendMain method to the requestBody object and use it as a parameter to the PostAsync method.
If you want to know more detailed information, you can check out this link:
https://learn.microsoft.com/en-us/graph/api/user-sendmail?view=graph-rest-1.0&tabs=csharp
Hope this helps.
If the reply is helpful, please click Accept Answer and kindly upvote it. If you have additional questions about this answer, please click Comment.