.NET GraphServiceClient发送邮件代码报错及无效果问题求助

一、高版本SDK的语法错误 #

我参考VB.NET的SMTP邮件发送示例，改写为C#代码如下：

static async Task SendEmail()
{
    var scopes = new[] { "https://graph.microsoft.com/.default" };

    var tenantId = "";
    var clientId = "";
    var clientSecret = "";

    var options = new TokenCredentialOptions
    {
        AuthorityHost = AzureAuthorityHosts.AzurePublicCloud
    };

    var clientSecretCredential = new ClientSecretCredential(tenantId, clientId, clientSecret, options);
    var graphClient = new GraphServiceClient(clientSecretCredential, scopes);

    var message = new Message
    {
        Subject = "This is the subject line",
        Body = new ItemBody
        {
            ContentType = BodyType.Text,
            Content = "This is the body of the email message."
        },
        ToRecipients = new List<Recipient>
        {
            new Recipient
            {
                EmailAddress = new EmailAddress
                {
                    Address = "user@domain.com"
                }
            }
        }
    };

    await graphClient.Users["myuser@mydomain.com"].SendMail(message, null).Request().PostAsync();
}

运行时出现错误：

Severity    Code    Description Project File    Line    Suppression State
Error   CS1955  Non-invocable member 'UserItemRequestBuilder.SendMail' cannot be used like a method.    MailSend    

错误行：await graphClient.Users["myuser@mydomain.com"].SendMail(message, null).Request().PostAsync();
推测旧版本SDK中该代码有效，但我对.NET和Graph SDK不熟悉，不知道怎么修复。

二、降级到Graph SDK v4后的运行异常 #

降级到SDK 4版本后，代码无语法错误，但无法正常运行：

using Azure.Identity;
using Microsoft.Graph;

namespace MailSend1
{
    internal class Program
    {
        static void Main(string[] args)
        {
            await SendEmail();
        }

        public static async Task SendEmail()
        {
            var scopes = new[] { "https://graph.microsoft.com/.default" };

            var tenantId = "";
            var clientId = "";
            var clientSecret = "";

            var options = new TokenCredentialOptions
            {
                AuthorityHost = AzureAuthorityHosts.AzurePublicCloud
            };

            var clientSecretCredential = new ClientSecretCredential(tenantId, clientId, clientSecret, options);
            var graphClient = new GraphServiceClient(clientSecretCredential, scopes);

            var message = new Message
            {
                Subject = "Just a test!",
                Body = new ItemBody
                {
                    ContentType = BodyType.Text,
                    Content = "Does it work?"
                },
                ToRecipients = new List<Recipient>
                {
                    new Recipient
                    {
                        EmailAddress = new EmailAddress
                        {
                            Address = "someuser@gmail.com"
                        }
                    }
                }
            };

            Console.WriteLine("Mail TO BE sent!");
            bool saveToSentItems = true;

            // 指定发送邮件的租户内用户账号
            await graphClient.Users["test@somedomain.net"].SendMail(message, saveToSentItems).Request().PostAsync();

            Console.WriteLine("Mail sent!");
        }
    }
}

程序运行后，邮件未发送，无错误提示，且第二个Console.WriteLine("Mail sent!");从未执行，请问问题出在哪里？

问题1：高版本SDK语法错误的修复 #

在Microsoft Graph SDK v5及以上版本中，SendMail的调用方式发生变化，不再使用链式的Request().PostAsync()，而是直接调用PostAsync()方法，且参数需封装为SendMailPostRequestBody对象。修正后代码：

await graphClient.Users["myuser@mydomain.com"].SendMail.PostAsync(new SendMailPostRequestBody
{
    Message = message,
    SaveToSentItems = null
});

问题2：SDK v4版本运行无响应的修复 #

1. 修正Main方法的异步处理
   你的Main方法是同步方法，直接调用await会导致程序阻塞，需将Main改为异步：

static async Task Main(string[] args)
{
    await SendEmail();
}

2. 排查权限与配置

• 确认tenantId、clientId、clientSecret已正确填写，且Azure AD中已为服务主体授予Mail.Send应用权限并完成管理员同意。
• 确认发送账号test@somedomain.net存在于你的租户中，服务主体拥有代表该账号发信的权限。

3. 添加异常捕获排查错误
   在SendEmail方法中添加异常捕获，定位潜在问题：

public static async Task SendEmail()
{
    try
    {
        // 原有代码逻辑...
        await graphClient.Users["test@somedomain.net"].SendMail(message, saveToSentItems).Request().PostAsync();
        Console.WriteLine("Mail sent!");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"发送失败：{ex.Message}");
        if (ex.InnerException != null)
        {
            Console.WriteLine($"内部错误：{ex.InnerException.Message}");
        }
    }
}

内容的提问来源于stack exchange，提问作者Primoz