How to send emails from a .net core console application via Gmail API?

Question

I've created a console application to send confirmation messages from a gmail account as a cron job, initially it used mailkit but it's no longer working so I added an apikey to a new project on google developers console, then added Google.Apis.Gmail.v1 to my project and I'm trying to use it, this is I have so far.

using System;
using System.Diagnostics;
using System.Threading.Tasks;
using Google.Apis.Gmail.v1;
using Google.Apis.Gmail.v1.Data;
using Google.Apis.Services;

namespace sender
{
    class Program
    {
        static void Main(string[] args) {
            var gs = new GmailService(new BaseClientService.Initializer {
                    ApplicationName = "mi-app-sending-emails",
                    ApiKey = "AIzxxxx_E_xxxxxx-Hxxxxx"
                });
                Message b = new Message();
                b.Id = "sender@gmail.com";
                //code here
    
                gs.Users.Messages.Send(b, "customer@gmail.com");
         }
    }
}

It does not send any message and the documentation does not provide much information, can you please provide me some information about how to achieve this code to work?

Answer 1

First off you forgot execute.

var result = gs.Users.Messages.Send(b, "customer@gmail.com").Execute();

second API key wont work with the gmail api. Your going to need to be authorized

private static UserCredential GetUserCredential(string clientSecretJson, string userName, string[] scopes)
        {
            try
            {
                if (string.IsNullOrEmpty(userName))
                    throw new ArgumentNullException("userName");
                if (string.IsNullOrEmpty(clientSecretJson))
                    throw new ArgumentNullException("clientSecretJson");
                if (!File.Exists(clientSecretJson))
                    throw new Exception("clientSecretJson file does not exist.");

                // These are the scopes of permissions you need. It is best to request only what you need and not all of them               
                using (var stream = new FileStream(clientSecretJson, FileMode.Open, FileAccess.Read))
                {
                    string credPath = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
                    credPath = Path.Combine(credPath, ".credentials/", System.Reflection.Assembly.GetExecutingAssembly().GetName().Name);

                    // Requesting Authentication or loading previously stored authentication for userName
                    var credential = GoogleWebAuthorizationBroker.AuthorizeAsync(GoogleClientSecrets.Load(stream).Secrets,
                                                                             scopes,
                                                                             userName,
                                                                             CancellationToken.None,
                                                                             new FileDataStore(credPath, true)).Result;

                    credential.GetAccessTokenForRequestAsync();
                    return credential;
                }
            }
            catch (Exception ex)
            {
                throw new Exception("Get user credentials failed.", ex);
            }
        }

/// <summary>
    /// This method get a valid service
    /// </summary>
    /// <param name="credential">Authecated user credentail</param>
    /// <returns>GmailService used to make requests against the Gmail API</returns>
    private static GmailService GetService(UserCredential credential)
    {
        try
        {
            if (credential == null)
                throw new ArgumentNullException("credential");

            // Create Gmail API service.
            return new GmailService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = "Gmail Oauth2 Authentication Sample"
            });
        }
        catch (Exception ex)
        {
            throw new Exception("Get Gmail service failed.", ex);
        }
    }
}

If you check the documentation for message.send you will notice it states you need to be authorized to access this method. API Keys only work with public endpoints not private endpoints