I'm using C# Microsoft Graph to send an email but I'm facing the error "Object reference not set to an instance of an object" when I call the await graphClient.Me.SendMail(message).Request().PostAsync() method. I tried to call var request = graphClient.Me.SendMail(message).Request() first and see that the request object is not null but when I call request.PostAsync() it gives the error, so I think PostAsync() method has a problem or I am missing something.

I'm not sure that if we can use the access token from msal-browser to send an email in C#?

Here is the code workflow:

1. On the browser I call msalInstance.loginPopup(loginRequest) method to get accesstoken after user selects their outlook account.
2. Then I send the accesstoken from the client to the backend to send an email. But I'm facing the error at this step await graphClient.Me.SendMail(message).Request().PostAsync();

Notes: I want to send an email from the backend (C#) instead of javascript because I want to handle some logic code at the backend.

Here is SDK:

Then you need to modify your send email method like this, it worked for me:

    public async Task sendAsync() {
                var mesg = new Message
                {
                    Subject = "Meet for lunch?",
                    Body = new ItemBody
                    {
                        ContentType = BodyType.Text,
                        Content = "The new cafeteria is open."
                    },
                    ToRecipients = new List<Recipient>
                    {
                        new Recipient
                        {
                            EmailAddress = new EmailAddress
                            {
                                Address = "[email protected]"
                            }
                        }
                    },
                    Attachments = new MessageAttachmentsCollectionPage()
                };
                var temp = new MailContentModel
                {
                    message = mesg
                };
                var jsonStr = JsonSerializer.Serialize(temp);
                string token = "your_token";
                var httpClient = new HttpClient();
                httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
                HttpResponseMessage response = await httpClient.PostAsync("https://graph.microsoft.com/v1.0/me/sendMail", new StringContent(jsonStr, Encoding.UTF8, "application/json"));
            }

using Microsoft.Graph;

public class MailContentModel
    {
        public Message message { get; set; }
    }