c# – SmtpClient.Send不适用于linux环境

string host = "10.99.99.10";
int port = 25;
string userName = "user@user.com";
string password = "password";
string from = userName;

var client = new SmtpClient
{
    Host = host,Port = port,EnableSsl = false,DeliveryMethod = SmtpDeliveryMethod.Network,UseDefaultCredentials = false,Credentials = new NetworkCredential(userName,password)
};

MailMessage mailMessage = new MailMessage();
mailMessage.From = new MailAddress(from);
mailMessage.To.Add(userName);
mailMessage.Body = "This is test mail.";
mailMessage.Subject = "Testing";                
client.Send(mailMessage);

例外：发送邮件失败.

InnerExcepiton：

System.ComponentModel.Win32Exception (0x80004005): GSSAPI operation failed with error - An invalid status code was supplied (Unknown error).
   at System.Net.Security.NegotiateStreamPal.AcquireCredentialsHandle(String package,Boolean isServer,NetworkCredential credential)
   at System.Net.NTAuthentication.Initialize(Boolean isServer,String package,NetworkCredential credential,String spn,ContextFlagsPal requestedContextFlags,ChannelBinding channelBinding)
   at System.Net.Mail.SmtpNtlmAuthenticationModule.Authenticate(String challenge,Object sessionCookie,ChannelBinding channelBindingToken)
   at System.Net.Mail.SmtpConnection.SetContextAndTryAuthenticate(ISmtpAuthenticationModule module,ContextAwareResult context)
   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)

堆栈跟踪：

at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at MyProject.Helper.Utils.SendMail() in C:TestMyProjectMyProject.HelperUtils.cs:line 146

Linux：Ubuntu 16.04.3 LTS

这是一个控制台应用程序.
为什么不在linux环境下工作？