Send email using Graph API from service account

Question

I am working on task in ASP.NET Core 5 (C#) which requires to send an email using Graph API, I have referred to following article and did the configuration on the Azure trial account and was able to send the emails.

Sending e-mails with Microsoft Graph using .NET

This is the send email code:

//send email
var client = await GetAuthenticatedGraphClient();
    
await client.Users[senderObjectId]
                  .SendMail(graphMailMessage, true)
                  .Request()
                  .PostAsync();

senderObjectId - Object Id coming from config

We deployed the same code on the client's Azure account we needed the User Object Id for the service account that we are going to use as a sender's email id. However, the client came back saying that the account is not part of the Azure AD and its a service account. Is there a way of sending emails without using the user object id.

Answer 1

Here's the method which takes parameters for mail sending. Also, it separates (comma) the mail and sends it to multiple users

    public string SendEmail(string fromAddress, string toAddress, string CcAddress, string subject, string message, string tenanatID , string clientID , string clientSecret)
    {
            try
            {

                var credentials = new ClientSecretCredential(
                                    tenanatID, clientID, clientSecret,
                                new TokenCredentialOptions { AuthorityHost = AzureAuthorityHosts.AzurePublicCloud });
                GraphServiceClient graphServiceClient = new GraphServiceClient(credentials);


                string[] toMail = toAddress.Split(',');
                List<Recipient> toRecipients = new List<Recipient>();
                int i = 0;
                for (i = 0; i < toMail.Count(); i++)
                {
                    Recipient toRecipient = new Recipient();
                    EmailAddress toEmailAddress = new EmailAddress();

                    toEmailAddress.Address = toMail[i];
                    toRecipient.EmailAddress = toEmailAddress;
                    toRecipients.Add(toRecipient);
                }

                List<Recipient> ccRecipients = new List<Recipient>();
                if (!string.IsNullOrEmpty(CcAddress))
                {
                    string[] ccMail = CcAddress.Split(',');
                    int j = 0;
                    for (j = 0; j < ccMail.Count(); j++)
                    {
                        Recipient ccRecipient = new Recipient();
                        EmailAddress ccEmailAddress = new EmailAddress();

                        ccEmailAddress.Address = ccMail[j];
                        ccRecipient.EmailAddress = ccEmailAddress;
                        ccRecipients.Add(ccRecipient);
                    }
                }
                var mailMessage = new Message
                {
                    Subject = subject,

                    Body = new ItemBody
                    {
                        ContentType = BodyType.Html,
                        Content = message
                    },
                    ToRecipients = toRecipients,
                    CcRecipients = ccRecipients

                };
                // Send mail as the given user. 
                graphServiceClient
                   .Users[fromAddress]
                    .SendMail(mailMessage, true)
                    .Request()
                    .PostAsync().Wait();

                return "Email successfully sent.";

            }
            catch (Exception ex)
            {

                return "Send Email Failed.\r\n" + ex.Message;
            }
    }