How to create a Gmail API Message

Question

I'd like to send a Message using Google's Gmail API. I've authenticated successfully, and am trying to use GmailService to send a message.

I'd like to use this:

myService.Users.Messages.Send(myMessage, "me").Execute();

where myService is a Google.Apis.Gmail.v1.GmailService and myMessage is a Google.Apis.Gmail.v1.Data.Message.

myService is fine, I've done the OAuth dance. I can get messages from my Inbox and all that. But I don't know how to construct myMessage. I have a standard .NET MailMessage, with human-readable Subject, Body, To, From etc.

But the Google Message class takes fields Payload or Raw. What's the easiest way to convert a full MailMessage to a string which I can set to the Payload or Raw properties? Or is this not what I should be doing at all?

The documentation for the Message class.

Answer 1

I found a solution. Strangely, .NET doesn't seem to support this natively/easily. There's a nice nuget package though, called AE.Net.Mail, which can write an easy-to-create message object to a stream.

Here's the sample code that pointed me in that direction.

Copy-and-pasted code as site seems to be down, and Google's cache might not last forever:

using System.IO;
using System.Net.Mail;
using Google.Apis.Gmail.v1;
using Google.Apis.Gmail.v1.Data;

public class TestEmail {

  public void SendIt() {
    var msg = new AE.Net.Mail.MailMessage {
      Subject = "Your Subject",
      Body = "Hello, World, from Gmail API!",
      From = new MailAddress("[you]@gmail.com")
    };
    msg.To.Add(new MailAddress("[email protected]"));
    msg.ReplyTo.Add(msg.From); // Bounces without this!!
    var msgStr = new StringWriter();
    msg.Save(msgStr);

    var gmail = new GmailService(Context.GoogleOAuthInitializer);
    var result = gmail.Users.Messages.Send(new Message {
      Raw = Base64UrlEncode(msgStr.ToString())
    }, "me").Execute();
    Console.WriteLine("Message ID {0} sent.", result.Id);
  }

  private static string Base64UrlEncode(string input) {
    var inputBytes = System.Text.Encoding.UTF8.GetBytes(input);
    // Special "url-safe" base64 encode.
    return Convert.ToBase64String(inputBytes)
      .Replace('+', '-')
      .Replace('/', '_')
      .Replace("=", "");
  }
}

Answer 2

Here is an alternative version using using MimeKit.

public void SendEmail(MyInternalSystemEmailMessage email)
{
    var mailMessage = new System.Net.Mail.MailMessage();
    mailMessage.From = new System.Net.Mail.MailAddress(email.FromAddress);
    mailMessage.To.Add(email.ToRecipients);
    mailMessage.ReplyToList.Add(email.FromAddress);
    mailMessage.Subject = email.Subject;
    mailMessage.Body = email.Body;
    mailMessage.IsBodyHtml = email.IsHtml;

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

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

    var gmailMessage = new Google.Apis.Gmail.v1.Data.Message {
        Raw = Encode(mimeMessage.ToString())
    };

    Google.Apis.Gmail.v1.UsersResource.MessagesResource.SendRequest request = service.Users.Messages.Send(gmailMessage, ServiceEmail);

    request.Execute();
}

public static string Encode(string text)
{
    byte[] bytes = System.Text.Encoding.UTF8.GetBytes(text);

    return System.Convert.ToBase64String(bytes)
        .Replace('+', '-')
        .Replace('/', '_')
        .Replace("=", "");
}

Note: If you are getting an email bounce issue, it is likely due to not setting the ReplyToList field. See: GMail API Emails Bouncing

Answer 3

C# Code for Gmail API Message (send email)

   namespace GmailAPIApp
   {
        class SendMail
        {
              static string[] Scopes = { GmailService.Scope.GmailSend };
              static string ApplicationName = "Gmail API .NET Quickstart";

             static void Main(string[] args)
             {
                UserCredential credential;

                using (var stream =
                new FileStream("credentials_dev.json", FileMode.Open, 
                  FileAccess.Read))
                {
                   string credPath = "token_Send.json";
                   credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                                GoogleClientSecrets.Load(stream).Secrets,
                                 Scopes,
                                 "user",
                                 CancellationToken.None,
                                 new FileDataStore(credPath, true)).Result;
                 Console.WriteLine("Credential file saved to: " + credPath);
               }

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

        // Define parameters of request.           
        string plainText = "To:[email protected]\r\n" +
                         "Subject: Gmail Send API Test\r\n" +
                         "Content-Type: text/html; charset=us-ascii\r\n\r\n" +
                         "<h1>TestGmail API Testing for sending <h1>";                          

        var newMsg = new Google.Apis.Gmail.v1.Data.Message();
        newMsg.Raw = SendMail.Base64UrlEncode(plainText.ToString());
        service.Users.Messages.Send(newMsg, "me").Execute();
        Console.Read();
    }
    private static string Base64UrlEncode(string input)
    {
        var inputBytes = System.Text.Encoding.UTF8.GetBytes(input);
        // Special "url-safe" base64 encode.
        return Convert.ToBase64String(inputBytes)
          .Replace('+', '-')
          .Replace('/', '_')
          .Replace("=", "");
        }
    }   
 }