Sending Email Using Asp.Net with C# aspx

SFAResponse
function PrintAck()
{
var str = "Invoice.aspx?From=Goa003fswQrtytioVsfgswzadf+33ff&View=redfgheesj45shy$ddvfds+4fff&PaymentMode=CC&PaymentMstId=" + document.getElementById("hidPaymentTranId").value
document.location.href=str;
}

function CancelClick()
{
var str ="Payment_Confirmation.aspx?From=Goa003fgswQrtyioVsfggswzadf+33ff&View=redfghedesj45shy$ddvfds+4fff&PaymentMode=CC&PaymentMstId=" + document.getElementById("hidPaymentTranId").value
document.location.href=str;
}
Hi 
Sending email using asp.net with C# aspx page it gives me error like 

The server rejected one or more recipient addresses. The server response
was: 550 5.7.1 Unable to relay for aaa@bbb.com
 
My code in aspx page
 
public void fncSendEmail(string strBody, string strSubject, string strToAddress, string strFr ...