Unable to send email via Microsoft Graph API (C# Console)

Question

I followed these 2 links to create a console app for sending emails using Graph API:

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

Microsoft Graph API unable to Send Email C# Console

I have added & granted the required permissions in Azure AD app:

I made sure to provide the client id, tenant id, client secret.

However, I see this error on running the console:

What am I missing?

Here is the code I tried from Microsoft Graph API unable to Send Email C# Console

static void Main(string[] args)
    {
        // Azure AD APP
        string clientId = "<client Key Here>";
        string tenantID = "<tenant key here>";
        string clientSecret = "<client secret here>";

        Task<GraphServiceClient> callTask = Task.Run(() => SendEmail(clientId, tenantID, clientSecret));
        // Wait for it to finish
        callTask.Wait();
        // Get the result
        var astr = callTask;
    }

    public static async Task<GraphServiceClient> SendEmail(string clientId, string tenantID, string clientSecret)
    {

        var confidentialClientApplication = ConfidentialClientApplicationBuilder
            .Create(clientId)
            .WithTenantId(tenantID)
            .WithClientSecret(clientSecret)
            .Build();

        var authProvider = new ClientCredentialProvider(confidentialClientApplication);       

        var graphClient = new GraphServiceClient(authProvider);

        var 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 = "myToEmail@gmail.com"
                    }
                }
            },
            CcRecipients = new List<Recipient>()
            {
                new Recipient
                {
                    EmailAddress = new EmailAddress
                    {
                        Address = "myCCEmail@gmail.com"
                    }
                }
            }
        };

        var saveToSentItems = true;

          await graphClient.Me
            .SendMail(message, saveToSentItems)
            .Request()
            .PostAsync();

        return graphClient;

    }

Answer 1

Based on your code which generates the confidentialClientApplication, you are using Client credentials provider.

But the way you send the email is:

await graphClient.Me
.SendMail(message, saveToSentItems)
.Request()
.PostAsync()

It is calling https://graph.microsoft.com/v1.0/me/sendMail in fact.

But Client credentials flow doesn't support /me endpoint. You should call https://graph.microsoft.com/v1.0/users/{id | userPrincipalName}/sendMail endpoint in this case.

So the code should be:

await graphClient.Users["{id or userPrincipalName}"]
    .SendMail(message, saveToSentItems)
    .Request()
    .PostAsync();

Or if you want to use /me/sendMail, choose Authorization code provider, where you should implement interactive login.

You can learn about the scenarios and differences between authorization code flow and client credentials flow.