我正在嘗試通過 .net 核心中的 SmtpClient 發送郵件?；旧衔抑皇菍⒁恍┡f的 .net 框架代碼遷移到 .net 核心。在舊系統中，它通過以下方式完成：using (var smtpClient = new SmtpClient("smtp.xyz.de", 587)){   smtpClient.UseDefaultCredentials = false;   smtpClient.Credentials = new System.Net.NetworkCredential("user", "password", "domain");   smtpClient.EnableSsl = true;   smtpClient.Send(mailMessage);}這段代碼工作正?！，F在我將此代碼遷移到 .net 核心，如下所示： using (var smtpClient = new SmtpClient("smtp.xyz.de", 587)) {    smtpClient.UseDefaultCredentials = false;    smtpClient.Credentials = new NetworkCredential("user", "password", "domain");    smtpClient.EnableSsl = true;      smtpClient.Send(mailMessage); }第一個問題是現在我收到一條錯誤消息：輸入不是有效的 Base-64 字符串，因為它包含非 base 64 字符、兩個以上的填充字符或填充字符中的非法字符。堆棧跟蹤：   at System.Convert.FromBase64CharPtr(Char* inputPtr, Int32 inputLength)   at System.Convert.FromBase64String(String s)   at System.Net.Mail.SmtpNegotiateAuthenticationModule.GetSecurityLayerOutgoingBlob(String challenge, NTAuthentication clientContext)   at System.Net.Mail.SmtpNegotiateAuthenticationModule.Authenticate(String challenge, NetworkCredential credential, Object sessionCookie, String spn, ChannelBinding channelBindingToken)   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)   at System.Net.Mail.SmtpClient.GetConnection()   at System.Net.Mail.SmtpClient.Send(MailMessage message)由于該錯誤，我嘗試將用戶和密碼字符串轉換為 Base64，如下所示：using (var smtpClient = new SmtpClient("smtp.xyz.de", 587)){   var userEncoded = Convert.ToBase64String(Encoding.UTF8.GetBytes("user"));   var passwordEncoded = convert.ToBase64String(Encoding.UTF8.GetBytes("password"));   smtpClient.UseDefaultCredentials = false;   smtpClient.Credentials = new NetworkCredential(userEncoded, passwordEncoded, "domain");   smtpClient.EnableSsl = true;                  smtpClient.Send(mailMessage);              }這樣做我得到另一個錯誤：SMTP 服務器需要安全連接或客戶端未通過身份驗證。服務器響應為：5.7.1 客戶端未通過身份驗證