System.Net.Mail.SmtpClient是否支持CRAM-MD5身份验证？

System.Net.Mail.SmtpClient 是 .NET Framework 中用于发送电子邮件的类。根据官方文档，System.Net.Mail.SmtpClient 类不支持 CRAM-MD5 身份验证。但是，您可以通过实现自定义的身份验证方法来支持 CRAM-MD5 身份验证。

以下是一个使用 CRAM-MD5 身份验证的示例代码：

using System;
using System.Net;
using System.Net.Mail;
using System.Security.Cryptography;

public class CramMd5Authentication : ICredentialsByHost
{
    private readonly string _username;
    private readonly string _password;

    public CramMd5Authentication(string username, string password)
    {
        _username = username;
        _password = password;
    }

    public NetworkCredential GetCredential(string host, int port, string authenticationType)
    {
        return new NetworkCredential(_username, _password);
    }

    public string Authenticate(string challenge, string userName, string password)
    {
        string[] parts = challenge.Split(' ');
        byte[] decodedChallenge = Convert.FromBase64String(parts[1]);
        string response = ComputeMd5Hash(decodedChallenge, userName, password);
        return "CRAM-MD5 " + Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(userName + " " + response));
    }

    private string ComputeMd5Hash(byte[] decodedChallenge, string userName, string password)
    {
        HMACMD5 hmacMd5 = new HMACMD5(System.Text.Encoding.ASCII.GetBytes(password));
        byte[] hashedBytes = hmacMd5.ComputeHash(decodedChallenge);
        string hashedString = BitConverter.ToString(hashedBytes).Replace("-", "").ToLower();
        return hashedString;
    }
}

您可以使用此类来实现 CRAM-MD5 身份验证，如下所示：

string from = "sender@example.com";
string to = "recipient@example.com";
string subject = "Test email";
string body = "This is a test email.";

MailMessage message = new MailMessage(from, to, subject, body);

SmtpClient client = new SmtpClient("smtp.example.com");
client.Credentials = new CramMd5Authentication("username", "password");

client.Send(message);

请注意，CRAM-MD5 身份验证可能存在安全风险，因此在使用此方法时要谨慎。