i get an InvalidOperationException when calling GraphServiceClient.Users[].SendMail.PostAsync()

Question

I have simple code like this:

			// Ensure client isn't null
			_ = _appClient ??
				throw new System.NullReferenceException("Graph has not been initialized for app-only auth");

			var requestBody = new SendMailPostRequestBody {
				Message = 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 = "******@contoso.com"
							}
						}
					}
				}
			};

			await _appClient.Users[_msGraphSettings.UserId].SendMail.PostAsync(requestBody);

I get a InvalidOperationException on the PostAsync():

Content type text/html does not have a factory registered to be parsed

requestBody is of type Microsoft.Graph.Users.Item.SendMail.SendMailPostRequestBody

I am using App Only Auth. Examples in the documentation only show variants of Me.SendMail. This gives its own errors when using with App Only Auth.

What am i doing wrong? And why is it so hard to find any documentation on this?

Answer 1

Hello Gideon EZ Access,

Thank you for reaching out to Microsoft Support!

For your problem, we have conducted a test and it runs well. The cause of your error should be the import of the wrong package. My code is as follows, please refer to it:

// The client credentials flow requires that you request the
// /.default scope, and pre-configure your permissions on the
// app registration in Azure. An administrator must grant consent
// to those permissions beforehand.
using Azure.Identity;
using Microsoft.Graph;
using Microsoft.Graph.Models;
using Microsoft.Graph.Users.Item.SendMail;
var scopes = new[] { "https://graph.microsoft.com/.default" };
// Values from app registration
var clientId = "client";
var tenantId = "tenantId";
var clientSecret = "clientSecret";
// using Azure.Identity;
var options = new ClientSecretCredentialOptions
{
    AuthorityHost = AzureAuthorityHosts.AzurePublicCloud,
};
// https://learn.microsoft.com/dotnet/api/azure.identity.clientsecretcredential
var clientSecretCredential = new ClientSecretCredential(
    tenantId, clientId, clientSecret, options);
var graphClient = new GraphServiceClient(clientSecretCredential, scopes);
var requestBody = new SendMailPostRequestBody
{
    Message = 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 = "******@xxxxx.onmicrosoft.com",
                },
            },
        }
    },
    SaveToSentItems = false,
};
await graphClient.Users["******@xxxx.OnMicrosoft.com"].SendMail.PostAsync(requestBody);

Reference document:

https://learn.microsoft.com/en-us/graph/api/user-sendmail?view=graph-rest-1.0&tabs=csharp

Hope this helps.

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