How to send email using service account details only in ASP.NET Core console application?

Question

I have gmail API service account details = client id and service account. How can I just send an email from one id to other without OAuth?

I want to authorize this email sending process with the service account credentials only.

Is there a nuget package that can help fulfill this requirement?

Answer 1

How can I just send an email from one id to other without OAuth?

I assume what you mean is how to send an email with out poping up the Oauth2 consent screen.

Using a service account will allow you to do that, once you have configured the permissions properly in your google workspace account. You grant the service account to preform actions on behalf of one of your domain users. This way the service account can send emails as that user without the user having to consent to that access because you have pre authorized it via google workspace.

The following code will show you how to authorize your application to use a service account.

class Program
    {
        public static string Base64Encode(string plainText)
        {
            var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
            return System.Convert.ToBase64String(plainTextBytes);
        }

    public static void SendMail()
    {
        try
        {
            string ApplicationName = "Gmail API .NET Quickstart";
            const string serviceAccount = "xxxx@xxxx-api.iam.gserviceaccount.com";

            var certificate = new X509Certificate2(@"c:\XXXX.p12", "notasecret", X509KeyStorageFlags.Exportable);

            var gsuiteUser = "YourDomain@YourDomain.com";

            var serviceAccountCredentialInitializer = new ServiceAccountCredential.Initializer(serviceAccount)
            {
                User = gsuiteUser,
                Scopes = new[] { GmailService.Scope.GmailSend, GmailService.Scope.GmailLabels }

            }.FromCertificate(certificate);

            var credential = new ServiceAccountCredential(serviceAccountCredentialInitializer);
            if (!credential.RequestAccessTokenAsync(CancellationToken.None).Result)
                throw new InvalidOperationException("Access token failed.");

            var service = new GmailService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });

            var mailMessage = new MailMessage();
            mailMessage.From = new MailAddress("se@Yourdomain.com");
            mailMessage.To.Add("ddddd@hotmail.com");
            mailMessage.ReplyToList.Add("se@Yourdomain.com");
            mailMessage.Subject = "test";
            mailMessage.Body = "<h1>sdf</h1>";
            mailMessage.IsBodyHtml = true;

            //foreach (System.Net.Mail.Attachment attachment in email.Attachments)
            //{
            //    mailMessage.Attachments.Add(attachment);
            //}

            var mimeMessage = MimeKit.MimeMessage.CreateFromMailMessage(mailMessage);

            var gmailMessage = new Message
            {
                Raw = Base64Encode(mimeMessage.ToString())
            };

            Message message1 = new Message();
            UsersResource.MessagesResource.SendRequest sendRequest = service.Users.Messages.Send(gmailMessage, "me");
            var s = sendRequest.Execute();


            Console.WriteLine("Message delivered!");
        }
        catch (Exception ep)
        {
            Console.WriteLine(ep.ToString());
        }
    }

The trick is to remember to set up the domain wide delegation properly and to decide which user the service account is going to be impersonating and to remember to add that email

without google workspace

If you do not have a google workspace account then you can not use service accounts. You may want to consider going though the smtp server instead.