要使用服务帐户详细信息发送电子邮件，需要在ASP.NET Core应用程序中安装Google.Apis.Auth和Google.Apis.Gmail.v1 NuGet包。在代码示例中，以下信息需要替换为自己的服务帐户详细信息：

• serviceAccountEmail：服务帐户电子邮件地址
• privateKey：服务帐户的私钥

代码示例：

using Google.Apis.Auth.OAuth2;
using Google.Apis.Gmail.v1;
using Google.Apis.Gmail.v1.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;

namespace ConsoleApp
{
    class Program
    {
        static string[] Scopes = { GmailService.Scope.GmailSend };
        static string ApplicationName = "Gmail API .NET Core";

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

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

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

            Message message = new Message();

            message.Raw = Base64UrlEncode(CreateMessageWithEmail(CreateEmail()));

            try
            {
                Message sendMessageResponse = service.Users.Messages.Send(message, "me").Execute();
            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: " + e.Message);
            }
        }

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