Issue with sending mails using Graph API

Question

Hello Team,

I am trying to send a mail using Graph API using asp.net core c# and i am getting the following error

ServiceException: Code: BadRequest
Message: Current authenticated context is not valid for this request. This occurs when a request is made to an endpoint that requires user sign-in. For example, /me requires a signed-in user. Acquire a token on behalf of a user to make requests to these endpoints. Use the OAuth 2.0 authorization code flow for mobile and native apps and the OAuth 2.0 implicit flow for single-page web apps.

I have created an Application Registration and also granted the following API permissions.
Microsoft Graph:

• Directory.Read.All
• Application.ReadWrite.OwnedBy
• Mail.Send
  Azure AD:
• Directory.Read.All
• Application.ReadWrite.OwnedBy

I am using this code
IConfidentialClientApplication confidentialClientApplication = ConfidentialClientApplicationBuilder
.Create(clientId)
.WithTenantId(tenantID)
.WithClientSecret(clientSecret)
.Build();

ClientCredentialProvider authProvider = new ClientCredentialProvider(confidentialClientApplication);

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

        var saveToSentItems = true;  

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

        return graphClient;  

Can someone help in fixing this issue.

Answer 1

You're targeting the /me endpoint which is not available using application credentials. You need to specify the user account that will be used to send the message.

await graphClient.Users["<user id or upn>"]
    .SendMail(message, saveToSentItems)
    .Request()
    .PostAsync();

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Answer 2

Is there away where i can send mails on behalf of a shared o365 mailbox , where i am seeing the shared mailbox as a Group in AAD ?