mail sending failure error msg Transaction failed. The server response was: 5.7.1 <unknown[192.168.140.116]>: Client host rejected: Access denied

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C#

SMTP

mail

SmtpClient

hi tech guys
i am facing a issue while sending mail through my C# code
The error msg thrown after this this execution is smClient.Send(Msg);
"Transaction failed. The server response was: 5.7.1 <unknown[192.168.140.116]>: Client host rejected: Access denied"
can anybody help me

public string SendOTPEmail(string EmailID, string OTP, string UserName)
       {
           string status = string.Empty;
           string EmailSending_Status = string.Empty;
           string UserId = string.Empty;
           string PassWord = string.Empty;
           string EmailFrom = string.Empty;
           string SMTPHost = string.Empty;
           string EmailDomain = string.Empty;
           System.Net.Mail.MailMessage Msg = new System.Net.Mail.MailMessage();
           try
           {
               {
                   UserId = "xyz";
                   PassWord = "abc";
                   EmailFrom = "abc@aaa.com";
                   EmailDomain ="aaa.com";
                   NetworkCredential basicAuthenticationInfo = new NetworkCredential(UserId, PassWord, EmailDomain);
                   SMTPHost = "abc.com";
                   string EmailFromName = "aaa.aa@ssss.com";
                   Msg.Subject = "Please complete your customer registration";
                   Msg.From = new System.Net.Mail.MailAddress(EmailFrom, EmailFromName);
                   Msg.To.Add(new System.Net.Mail.MailAddress(EmailID));
                   Msg.IsBodyHtml = true;
                   Msg.Body = " Dear Sir/Madam," + "" + "<br>" +
                                   "" + "<br>" +
                                     "TATA AIG General Insurance welcomes you to its Portal." + "" + "<br>" +
                                    "Please enter the One Time Password:" + OTP + " to complete your Registration " + "" + "" + "<br>" +
                                    "This One Time Password is valid for 24 hours." + "" + "<br>" +
                                      "" + "<br>" +
                                     "" + "<br>" +
                                "Thanks and Regards" + "<br>" +
                               "Portal Admin" + "<br>" +
                                "" + "<br>" +
                                "" + "<br>" +
                                "" + "<br>" +
                                "Note: This is a system-generated e-mail. Please do not reply back.";
                   SmtpClient smClient = new SmtpClient();
                   smClient.Host = SMTPHost;
                   smClient.Port = 587;
                   smClient.EnableSsl = false;
                   smClient.UseDefaultCredentials = false;
                   smClient.Credentials = basicAuthenticationInfo;

                   if (ValidSMTP(SMTPHost))
                   {
                       smClient.Send(Msg);

                       EmailSending_Status = "sent";
                       status = "OTP sent to your Mailbox successfully.";
                   }
                   else
                   {
                       EmailSending_Status = "Mailserver Down";
                       status = "Failed";
                   }
               }
           }

           catch (SmtpException ex)
           {
               status = ex.Message;
               EmailSending_Status = "failed";
           }
           return status;
       }