system.net.mail 发送邮件有关问题（急）

system.net.mail 发送邮件问题（急在线等！）
在公司测试没问题，拿到客户那里出现以下异常：

    System.Net.Mail.SmtpException:   Failure   sending   mail.   --->   System.FormatException:   Invalid   length   for   a   Base-64   char   array.
      at   System.Convert.FromBase64String(String   s)
      at   System.Net.NTAuthentication.GetOutgoingBlob(String   incomingBlob)
      at   System.Net.Mail.SmtpNtlmAuthenticationModule.Authenticate(String   challenge,   NetworkCredential   credential,   Object   sessionCookie)
      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)
      ---   End   of   inner   exception   stack   trace   ---
      at   System.Net.Mail.SmtpClient.Send(MailMessage   message)
      at   _Default.sendmail()   in   c:\WebSite2\Default.aspx.cs:line   90 ');

问题解决马上结帐！！

[解决办法]

问题解决``是SMTP验证问题`